The command use to check if bridge are setup is not reliable.

On some plateform or verion of ovs the ouput of ovs-vsctl show have quote or not.
This patch implement a other method to check if bridge exist.

Co-Authored-By: Stephan Renatus <s.renatus@x-ion.de>
Change-Id: Iaae683213f281529e2167ac326d8e9573f026f12
Closes-Bug: #1266558