LU-3626 tests: More time to allow mds-ost sync being finished

LU-3626 tests: More time to allow mds-ost sync being finished

Because mds-ost unlink log synchronization is not enforced by any
timeout, so we will add more time to allow mds-ost sync being
finished in replay-single test_20b. And also add more information
in the tests to help us understand which MDT slow down the
synchronziation.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I5f63540e602ad29cd221de6dac0c22546629a9cd
Reviewed-on: http://review.whamcloud.com/7676
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>