This adds a script that allows one to pass in OpenStack objects
to fill in the eth/ip src/dst data when running ovn-trace. e.g.
$ ml2ovn-trace --from server=vm1 --to server=vm2
or
$ ml2ovn-trace --from server=vm1 --ip-dst 8.8.8.8 --via router=r1
Change-Id: I05c4eeee8d9cdb8faee2ee2eee166b421482173f