LU-11596 tests: wait for grant to stop changing

LU-11596 tests: wait for grant to stop changing

Wait for the client and server grant to stop changing in sanity
test-42d, test_64[acd] to avoid intermittent failures.

Test-Parameters: trivial testlist=sanity env=ONLY=64a,ONLY_REPEAT=100
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I3ef3a93d04e73ffb0098f712373c1462c53ebbe5
Reviewed-on: https://review.whamcloud.com/37876
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Wei Liu <sarah@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>