Adds _(prerun|check)_134 functions to test_migrations

The _prerun_134 function populates the 'bw_usage_cache'
table with real data, different in some critical ways,
before migrating it. _check_134 function certifies that
things were properly migrated.

Partially implements bp migration-testing-with-data

Change-Id: I4100c8aa3e1c9d2ff4fdb095dba4cb084b5df279
Update to simplified common oslo version code.

Based on https://review.openstack.org/#/c/19957/

Change-Id: Ieefee2af8812d0217e95eeffb3cf53d8e55c8fe6
Merge "Adds _(prerun|check)_134 functions to test_migrations"
Merge "Update to simplified common oslo version code."