restorecon call in RPM POSTIN script has hardcoded datadir path

Most of the POSTIN script uses the datadir setting from the MariaDB configuration files, so this can be set to a different path before installing the MariaDB-server RPM.

At the end of the POSTIN script we have the /var/lib/mysql data directory path hardcoded though:

if [ -x /sbin/restorecon ] ; then

  /sbin/restorecon -R /var/lib/mysql

fi

so with a changed datadir setting these log messages are issued:

/sbin/restorecon: lstat(/var/lib/mysql) failed: No such file or directory

warning: %post(MariaDB-server-10.6.18-1.el8.x86_64) scriptlet failed, exit status 255

Error in POSTIN scriptlet in rpm package MariaDB-server

Not critical as the MariaDB-server package gets fully installed nonetheless, but it raises questions.

No harm done by not actually running restorecon on the non-standard datadir either, as our SElinux policies would only have context for the default datadir anyway.

Maybe we should just add a simple

if test -d /var/lib/mysql

condition to that last code block