VMware: Network fallback in case specified one not found

In the case that opqaue network does not match the bridge ID then
we will fall back on a predefined network (configurable by the admin
via 'integration_bridge' in the 'vmware' section).

Fixes bug 1225002

(cherry picked from commit a0546fd3f42c37e8cd6e4e9b70d59ae1e689b4b7)

Change-Id: I7508a13f116b539fef1f771fc5ab4c32ffa520bc
Merge "VMware: Network fallback in case specified one not found" into milestone-proposed