Make procedure retry interval configurable in test

I think the problem is related to HBASE-22193, where we add exponential backoff when failing to open a region. Saw this in the output

2019-04-29 20:43:09,624 WARN  [PEWorker-24] assignment.TransitRegionStateProcedure(351): Failed transition, suspend 129secs pid=15, state=RUNNABLE:REGION_STATE_TRANSITION_GET_ASSIGN_CANDIDATE, hasLock=true; 

And the wait time is 180 seconds, so we time out...

Maybe we should introduce a max wait time config, and set it to a small value in this test...