LU-2189 tests: Ensure quiescence for sanityn/36

LU-2189 tests: Ensure quiescence for sanityn/36

Because sanityn/36 measures space used/free, ensure that all previous
operations have completed prior to getting statfs info.

Test-Parameters: mdtfilesystemtype=zfs ostfilesystemtype=zfs osscount=1 ostcount=2 mdscount=1 mdtcount=1 testlist=sanityn
Test-Parameters: mdtfilesystemtype=zfs ostfilesystemtype=zfs osscount=1 ostcount=2 mdscount=1 mdtcount=1 testlist=sanityn
Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: I684d428bbb6fca1a004bba5acf6a17a1636fb0dd
Reviewed-on: https://review.whamcloud.com/27373
Tested-by: Jenkins
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>