Extending Nova CLI to support forcing service to be set/unset as down,
as specified in blueprint mark-host-down.
Depends-On: I612582ba7b70bb6d167aa68bdfc47faa3b7b85ed
Depends-On: I39f1a84c100726f87a4dc464dd9922d66efdb53f
Implements: blueprint support-force-down-service
Change-Id: I2b80ac32a95fe80363b4ad95d8d89fff097935a3