Upgrade which fails suggesting FORCE_UPGRADE is not transactional, it installs some packages but not all

$ sudo yum install mysql-server mysql

...

Running Transaction

  Updating   : mysql-libs-5.1.73-5.el6_7.1.i686                                                                                  1/5 

  Installing : mysql-5.1.73-5.el6_7.1.i686                                                                                       2/5 

  Installing : perl-DBD-MySQL-4.013-3.el6.i686                                                                                   3/5 

  Installing : mysql-server-5.1.73-5.el6_7.1.i686                                                                                4/5 

  Cleanup    : mysql-libs-5.1.61-1.el6_2.1.i686                                                                                  5/5 

Installed:

  mysql.i686 0:5.1.73-5.el6_7.1                                 mysql-server.i686 0:5.1.73-5.el6_7.1                                

Dependency Installed:

  perl-DBD-MySQL.i686 0:4.013-3.el6                                                                                                  

Dependency Updated:

  mysql-libs.i686 0:5.1.73-5.el6_7.1                                                                                                 

Complete!

$ sudo yum install MariaDB-10.1.13-centos6-i686-server.rpm MariaDB-10.1.13-centos6-i686-client.rpm  MariaDB-10.1.13-centos6-i686-common.rpm  MariaDB-10.1.13-centos6-i686-compat.rpm

...

Dependencies Resolved

=====================================================================================================================================

 Package                    Arch             Version                          Repository                                        Size

=====================================================================================================================================

Installing:

 MariaDB-client             i686             10.1.13-1.el6                    /MariaDB-10.1.13-centos6-i686-client              46 M

     replacing  mysql.i686 5.1.73-5.el6_7.1

     replacing  mysql.i686 5.1.73-5.el6_7.1

 MariaDB-common             i686             10.1.13-1.el6                    /MariaDB-10.1.13-centos6-i686-common             226 k

 MariaDB-compat             i686             10.1.13-1.el6                    /MariaDB-10.1.13-centos6-i686-compat             7.1 M

     replacing  mysql-libs.i686 5.1.73-5.el6_7.1

     replacing  mysql-libs.i686 5.1.73-5.el6_7.1

 MariaDB-server             i686             10.1.13-1.el6                    /MariaDB-10.1.13-centos6-i686-server             187 M

     replacing  mysql-server.i686 5.1.73-5.el6_7.1

     replacing  mysql-server.i686 5.1.73-5.el6_7.1

Installing for dependencies:

 galera                     i686             25.3.15-1.rhel6.el6              galera                                           6.3 M

 lsof                       i686             4.82-5.el6                       base                                             319 k

 rsync                      i686             3.0.6-12.el6                     base                                             329 k

Transaction Summary

=====================================================================================================================================

Install       7 Package(s)

Total size: 247 M

Total download size: 6.9 M

Is this ok [y/N]: y

Running rpm_check_debug

Running Transaction Test

Transaction Test Succeeded

Running Transaction

  Installing : MariaDB-common-10.1.13-1.el6.i686                                                                                1/10 

  Installing : MariaDB-compat-10.1.13-1.el6.i686                                                                                2/10 

  Installing : MariaDB-client-10.1.13-1.el6.i686                                                                                3/10 

  Installing : galera-25.3.15-1.rhel6.el6.i686                                                                                  4/10 

  Installing : rsync-3.0.6-12.el6.i686                                                                                          5/10 

  Installing : lsof-4.82-5.el6.i686                                                                                             6/10 

Error in PREIN scriptlet in rpm package MariaDB-server-10.1.13-1.el6.i686

******************************************************************

A mysql-server-5.1.73-5.el6_7.1.i686 server package is installed. It might be not completely compatible

with MariaDB. Some files may be installed to different locations, including log

files and the service startup script in /etc/init.d/.

You can force the upgrade by setting the FORCE_UPGRADE=1 environment variable,

...

This is a brief description of the upgrade process.  Important details

can be found in the MariaDB manual, in the Upgrading section.

******************************************************************

error: %pre(MariaDB-server-10.1.13-1.el6.i686) scriptlet failed, exit status 1

error:   install: %pre scriptlet failed (2), skipping MariaDB-server-10.1.13-1.el6

  Erasing    : mysql-5.1.73-5.el6_7.1.i686                                                                                      8/10 

  Erasing    : mysql-libs-5.1.73-5.el6_7.1.i686                                                                                 9/10 

mysql-server-5.1.73-5.el6_7.1.i686 was supposed to be removed but is not!

Installed:

  MariaDB-client.i686 0:10.1.13-1.el6         MariaDB-common.i686 0:10.1.13-1.el6         MariaDB-compat.i686 0:10.1.13-1.el6        

Dependency Installed:

  galera.i686 0:25.3.15-1.rhel6.el6                 lsof.i686 0:4.82-5.el6                 rsync.i686 0:3.0.6-12.el6                

Replaced:

  mysql.i686 0:5.1.73-5.el6_7.1                                  mysql-libs.i686 0:5.1.73-5.el6_7.1                                 

Failed:

  MariaDB-server.i686 0:10.1.13-1.el6                              mysql-server.i686 0:5.1.73-5.el6_7.1                             

Complete!

$ rpm -qa | grep -iE 'mysql|maria'

perl-DBD-MySQL-4.013-3.el6.i686

MariaDB-compat-10.1.13-1.el6.i686

mysql-server-5.1.73-5.el6_7.1.i686

MariaDB-common-10.1.13-1.el6.i686

MariaDB-client-10.1.13-1.el6.i686