tests: fix dependency on sleep in bug-874498.t

With the introduction of http://review.gluster.org/4784, there are
delays which breaks bug-874498.t which wrongly depends on healing
to finish within 2 seconds.

Fix this by using 'EXPECT_WITHIN 60' instead of sleep 2.

BUG: 874498
Change-Id: I7131699908e63b024d2dd71395b3e94c15fe925c
Original-author: Anand Avati <avati@redhat.com>
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/4832
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>