LU-4306 tests: improve test_4a of s-q

LU-4306 tests: improve test_4a of s-q

test_4a of s-q used "sync; sleep 1; sync" to sync all data, that
could stall for an unexpected long time, this patch changes it
to sync_all_data for better time-efficiency.

This patch also modified the script to report proper error when
the grace has already expired before trying create new file.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: I4aa2f69933be37d5f98af8172ed6a20781fe6e38
Reviewed-on: http://review.whamcloud.com/15483
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>