Switch to oslo.concurrency

Change-Id: If4b47a292a5fcbf04c15a6f78d3c6ca7d89855e1
Remove module not really used by Ceilometer

This file should only list modules that Ceilometer directly imports, not
any dependency incured by using other oslo-incubator modules.

Change-Id: I5a45b2f28539c55f01834c913d262041d3b11267
Merge "Switch to oslo.concurrency"
Merge "Remove module not really used by Ceilometer"