SqlAlchemy 2.0 has gotten a lot more picky about transactions. In
addition to needing to explicitly set up transactions using SqlAlchemy
2.0 it seems alembic's get_current_revision() call cannot be in the same
transaction as the alembic migrate/stamp calls with MySQL 8.0.
In particular the get_current_revision call seems to get a
SHARED_HIGH_PRIO lock on the alembic_version table. This prevents the
migrate/stamp calls from creating the alembic_version table as this
requires an EXCLUSIVE lock. The SHARED_HIGH_PRIO lock appears to be in
place as long as the get_current_revision transaction is active. To fix
this we simplify our migration tooling and put get_current_revision in a
transaction block of its own. The rest of our migrate function calls
into functions that will setup new transactions and it doesn't need to
be in this block.
Change-Id: Ic71ddf1968610784cef72c4634ccec3a18855a0e
cfedda0c2f