tests: Avoid timing delays caused by fsync

Change-Id: I2da53dd14d7352bdc878fce5a9019a955e150ce9
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/5377
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>