Move sa-migrate experimental jobs to check/gate

These jobs have been tested in the experimental queue
for change I8c5d2874c83e7df46da69969ed54d85437c849e7
Now when we know they actually work, we can add them
to check/gate queues to be executed for all new changes
submitted to sqlalchemy-migrate.

Change-Id: I8d8b5fbf03dc90addde31879dcb88db5bf8122bb
Merge "Move sa-migrate experimental jobs to check/gate"