When running in the cloud, without KVM emulation, together with many
other tenants, it can take a very long time to boot the instances.
Therefore, add a meta test that will wait for all devices in the
physical topology to come up before exiting. This means that the
actual test cases that follow can assume that devices will answer
NETCONF requests.
Create topology objects that are tailored to represent topologies on
the expected format. This let's us make convenient accessors for
things like the controller node, infix devices, getting the ports used
to reach a certain device from another one, etc.
