engine : Update CoCo to use CommandContext

CommandCoordinator has been updated to find
Commands with CommandContext constructor.

RemoveSnapshotCommand and RemoveSnapshotSingleDiskLiveCommand
have been updated to call CoCo with context when
running child commands

Change-Id: Id914da3ed1a29e651ad2491fc88a2705b7af6e8f
Bug-Url: https://bugzilla.redhat.com/1115127
Signed-off-by: Ravi Nori <rnori@redhat.com>