rename oslo.concurrency to oslo_concurrency

oslo.concurrency-0.3.0 has moved its path to oslo_concurrency,
the old path oslo.concurrency can still work but is deprecated now.

Change-Id: I2b2b362f766bb82058af6f9ed92189165aa9a629
Closes-Bug: #1398656
Merge "rename oslo.concurrency to oslo_concurrency"