LU-2329 quota: wait longer in test_7c

LU-2329 quota: wait longer in test_7c

In test_7c of s-q, we'd wait longer than usual to make sure
the reintegration triggered by quota wb thread is done.

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I977b3a03a0e57424a531df13fed5550a753f41c2
Reviewed-on: http://review.whamcloud.com/4739
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Reviewed-by: Lai Siyao <laisiyao@whamcloud.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>