Fix race in CRD duplicates test

The CRD duplicates test was removing the job hold flag which meant all
FakeBuild threads were racing each other to update the FakeWorker
history. Avoid this by releasing jobs for one change at a time and
letting them settle before checking the job history list.

Change-Id: I86ee058546d2f0b833106725b419a8adcb1b7508
1 file changed