object-storage: use temp file optimization

A file name '.<FILENAME>.<RANDOM>' will hash to the same GlusterFS node
as a file named '<FILENAME>', thus avoiding creation/deletion of linkfiles on a rename.

This is part of the work needed to address BZ 876660
(https://bugzilla.redhat.com/show_bug.cgi?id=876660).

Change-Id: I6f18c14b8eaa7a35c96f7e455ef3a19bee7dbde5
BUG: 876660
Signed-off-by: Mohammed Junaid <junaid@redhat.com>
Reviewed-on: http://review.gluster.org/4325
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>
Reviewed-by: Peter Portante <pportant@redhat.com>