gluster: Fixed coverity scan failure in GetGlusterVolumeRebalanceStatusQueryTest

Fixed an coverity scan failure issue in the test case class
GetGlusterVolumeRebalanceStatusQueryTest.

Change-Id: I767f981cfefa8a783cc636e96cc32675fc17aefc
Signed-off-by: Shubhendu Tripathi <shtripat@redhat.com>