Stabilize bgp_xmpp_test

Use StateMachineTest and XmppStateMachineTest instead of the
base classes so that sessions can come up in timely manner.

Clean up includes and add a bit more tracing to the output.

Change-Id: I64f4fcefa481b46da15ccf9318fb00a655c053b5
Merge "Stabilize bgp_xmpp_test"