Add lockutils fixture to OpportunisticTestCase

We're getting hit hard with db race problems right now and the
proper fix can't go in until infra has all of their regions
updated.  Using the lock fixture to serialize all of the db tests
should help with the problem until infra is ready.

Change-Id: If883832b0eba08f1508a247310b8eebd67b27971
Partial-Bug: #1288916
Merge "Add lockutils fixture to OpportunisticTestCase"