vfs/glusterfs: in case atime is not passed, set it to the current atime

vfs/glusterfs: in case atime is not passed, set it to the current atime

The Linux CIFS client does not pass an updated atime when a write() is
done. This causes the vfs/glusterfs module to set the atime to -1 on the
Gluster backend, resulting in an atime far in the future (year 2106).

Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-by: Ira Cooper <ira@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Wed Jan 15 21:31:30 CET 2014 on sn-devel-104