engine: Support for gluster task monitoring

Added GlusterTasksSyncJob that periodically polls all
running gluster tasks and updates the corresponding step
and job with status and description.

If the task is completed
 - job is ended
 - lock on volume is released

Change-Id: Ica67b56804cbb892886160f0b22043687277d476
Signed-off-by: Sahina Bose <sabose@redhat.com>