[devstack] Remove bridge only if it's not OVB_PHYSICAL_BRIDGE
[devstack] Remove bridge only if it's not OVB_PHYSICAL_BRIDGE

In a scenario we want to deploy DevStack with ironic inspector for real
hardware and use OVS_PHYSICAL_BRIDGE for IRONIC_INSPECTOR_INTERFACE as
well we dont need to issue interface delete.

Change-Id: I45271ddc34b5e9d542b6a1499d698503717f5f03

openstack/ironic-inspector,openstack/ironic-inspector