Set external ID on br-ex

This will enable Neurtron identify that the external bridge is a
Neutron bridge (this is required for bug 1192883)

Change-Id: I8ad1b0b3d93d5068beec2021abf9afbacf8c48ff
Merge "Set external ID on br-ex"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp