Re-add sqlalchemy-migrate python 2.6 jobs

Re-add python 2.6 sqlalchemy-migrate check jobs. We should
keep these running as long as we support python 2.6 for libraries and
previous releases.

Change-Id: Iae875f8234cd9780470c137d284f14d914582c60
Merge "Re-add sqlalchemy-migrate python 2.6 jobs"