toptests/isis_sr_te_topo1: test out-of-order route/route-map changes

toptests/isis_sr_te_topo1: test out-of-order route/route-map changes

    A SR policy matches a BGP nexthop based on the IP address of
    the nexthop and the color of the route (color may be assigned
    to routes using a route-map).

    The order of events (BGP route arrival, route-map definition,
    policy and candidate-path definition) should not affect the
    matching/mapping.

    These changes add tests for:

	- removing/adding BGP route after policy and routemap are
	  defined and held constant

	- changing route map color to be different from policy color,
	  and then changing back to match

    after each change, the policy should be observed to be in effect
    unchanged from before, i.e., the route's nexthops should reflect
    the matching SR policy.

Signed-off-by: G. Paul Ziemba <paulz@labn.net>