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: I86629a81d55d88b67cdf0639dc9995887b516cca
Closes-Bug: #1398656
Merge "rename oslo.concurrency to oslo_concurrency"