Upgrade from 10.0 to 10.1 on Vivid does not work with normal source list

It's MDEV-5977 all over again, only the next generation of it – new Ubuntu, new MariaDB.

If MariaDB 10.0 is installed, even from MariaDB's own packages, and either vivid-security universe or vivid-updates universe are in the sources.list (which has both normally), installation of 10.1 mariadb-server fails in the same way as it did in MDEV-5977:

• mariadb-server fails to install pointing at mariadb-server-10.1;
• mariadb-server-10.1 fails to install pointing at mariadb-server-core-10.1;
• mariadb-server-core-10.1, if requested explicitly, installs all right and pulls other packages.

That's the reason of Buildbot's upgrade2 failures on Vivid:
http://buildbot.askmonty.org/buildbot/builders/kvm-deb-vivid-amd64/builds/201/steps/test_2/logs/stdio

So, there are two workarounds for the problem:

• disable vivid-security universe and vivid-updates universe to upgrade MariaDB;
• specify mariadb-server-core-10.1 on apt-get install command line.

None of these is good enough when 10.1 goes GA.