Correct value of $public_bridge_name

This patch corrects value of $public_ovs_bridge_name in provision_demo.pp template.

Change-Id: I6fb10e3dfb97a5e1d4d191cce5649d09f8649ab9
Closes-bug: #1360107
(cherry picked from commit c60d74b6b9d76571bb5a9583648e863236bede9a)
Merge "Correct value of $public_bridge_name" into icehouse