Migrate to oslo.concurrency

Migrate to oslo.concurrency

Namespaces are not used anymore, so imports are for oslo_concurrency,
not oslo.concurrency.

lockutils direct call is not supported anymore, so using shipped
lockutils-wrapper instead.

Use ExternalLockFixture to set lock_path for unit testing.

Updated cache and cache/_backends module from oslo-incubator to use
oslo.concurrency and not incubator version of lockutils module.

Dropped lockutils incubator module that is now moved to oslo.concurrency. Not
dropping fixture module that includes lockutils fixture since other fixtures
are still used in the tree.

Closes-Bug: #1387092
Change-Id: I2ba2295f8f5d55f272a9d23555940586b25b5a1c