Fix assert(invalid) in test_topology creation
Fix assert(invalid) in test_topology creation

Summary: In remove_host() : non-reachable host is checked against self.test_hosts, it should self.test_hosts.values().

Differential Revision: D6065571

fbshipit-source-id: dfdf216b8bca9fdb41e219ac9ce2dbea200bbea5

peterlei/fboss,peterlei/fboss,peterlei/fboss,peterlei/fboss