bug-979365.t: fix wrong expectation of encountering fsync

After the append-write detection patch, FSYNCs may or may not
be issued depeneding on the order in which writes reach the
server (in the presence of write-behind). Fix the test case
to understand this non-deterministic behavior.

Change-Id: I1dc3453a6dd4a12a66551948eb8311d789ac2ecf
BUG: 927146
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5694
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>