tests: Wait for convergence first

tests: Wait for convergence first

The test_bgp_multi_vrf_topo2.py script had a bunch
of places where it would change an interface status
or add delete routes that would affect bgp convergence
but it was never ensuring that convergence had happened
before the test verified the bgp rib.  I believe this
was leading to many intermittant ci failures in
testing for other PR's to be accepted.  Modify
the code to wait for bgp convergence if we just
made a change to the topology

Signed-off-by: Donald Sharp <sharpd@nvidia.com>