NSX: fix intermetting UT failure on vshield test_router_create

Logstash shows this happened twice during the past 24 hours.
Let's be proactive and see if we can mitigate the random failure
by raising the poll time.

Change-Id: Icef7de4d9fbb3da037337c607fd7642cc15e0257
Closes-bug: 1292506
Merge "NSX: fix intermetting UT failure on vshield test_router_create"