tests/quota: Wait till the rebalance is complete

Change-Id: Ia6f0c81fb1542ce1de965a69a61535691df056c3
BUG: 1077159
Signed-off-by: Varun Shastry <vshastry@redhat.com>
Reviewed-on: http://review.gluster.org/7380
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Justin Clift <justin@gluster.org>
Tested-by: Justin Clift <justin@gluster.org>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>