engine: Audit log for brick status change

During periodic sync of gluster with engine
if change in brick status is detected this
needs to be logged.

Added corresponding entries for event
notification

Change-Id: If1764dd5c41b484637595b0fa20598849f9ba347
Bug-Url: https://bugzilla.redhat.com/958813
Signed-off-by: Sahina Bose <sabose@redhat.com>