LU-11488 test: ignore statfs from precreate in sanity 133b()

LU-11488 test: ignore statfs from precreate in sanity 133b()

In sanity test_133b() use obdfilter client export stats rather than
target stats to check for statfs allowing us to ignore statfs RPCs
from the MDT for precreate.

Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: Ia47e535d6ce94c712da8ad8698315188c8d64d83
Reviewed-on: https://review.whamcloud.com/33517
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>