currently Heat sets the resource_id of the ExtraRoute resource to
`<router_id>:<destination>:<nexthop>`
and later parses destination and nexthop out from resource_id on delete
of the resource.
However colon is an integral part of IPv6 addresses, so such parsing
fails in this case.
In this patch we use actual resource properties to find
router_id, destination and nexthop, thus avoiding the parsing error.
Change-Id: I6835efc632c38aac3466d3952f8887ef15dbd0ad
Story: 2007085
Task: 38080
9ed61fc666