Try to ensure we'll have a truly random postfix

While it is very improbable, it seemed fairly straight forward to add
a small bit of code to ensure the temporary file name is random and
won't clash with another host, pid or thread potentially working on
the same object.

BUG: XXXXXX (https://bugzilla.redhat.com/show_bug.cgi?id=XXXXXX)

Change-Id: I862021b725efbfe58b98754c4470aef4882eb8f7
Signed-off-by: Peter Portante <peter.portante@redhat.com>
Reviewed-on: http://review.gluster.org/5671
Reviewed-by: Luis Pabon <lpabon@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>