change the way to filter stats for vhost from http api response.

Somehow, some times, rabbitmq http api fails to get a valid response
with vhost specified, works without vhost, so we filter the stats
for the monitored vhost from the response for all vhosts or api/queues/wq.

Change-Id: I95dbc9b0fca2af88bd6a46c4c112264c37b636c0
Merge "change the way to filter stats for vhost from http api response." into dev/experimental