fix mysql race in tests

because of testr, we can't assume the migrations tests run in
sequence, so they make run all at the same time. This is fine for
our in memory sqlite db, but when talking to a real external
database, not so good.

Since a second mysql test was added, we started racing on these
migrations them often hitting at the same time causing random fails
in gate.

Fix this by moving all the mysql tests into 1 test function, so we
won't race.

Fixes bug #1101874

Change-Id: I7627f3bd510266c99af018d355f960b352573759
Merge "fix mysql race in tests"