gluster: setting the step status to unknown.

when volume is up but gluster does not know of task, step
status is set to UNKNOWN. It is explicitly set as the task
status is already FINISHED and it is not set by method
markStepEnded.

https://bugzilla.redhat.com/show_bug.cgi?id=1027743
Change-Id: I9418cec0142e4c170a386d6568f6f624bb098985
Signed-off-by: ndarshan <dnarayan@redhat.com>