CLOUDSTACK-4262: Fix TestVPCNetworkGc.test_01_wait_network_gc

As per the test plan, after waiting for network gc
LB rules should be cleared. Added that check instead of router
being in stopped state.

Signed-off-by: venkataswamybabu budumuru <venkataswamybabu.budumuru@citrix.com>
(cherry picked from commit abdb84bb05abc9f2bd102bca1c1b34865f34d771)