engine:fail stop volume if remove brick is running

'stop' gluster volume is not allowed if there is a remove brick operation
is running on that volume

Change-Id: Ic7f227b086e78374b385ebd2f4d8f8591825c7fe
Bug-Url: https://bugzilla.redhat.com/1032020
Signed-off-by: Karnan TC <kchidamb@redhat.com>