Fix failing Nagios check for Parsoid Varnish

check_http_generic hits the URL /wikimedia-monitoring-test , which
results in a 404 for this particular service. Switch to
check_http_on_port, which checks / , which should get a 200 as intended.

Change-Id: I030ffe69e9204c79b7009c789473a27651b3c7e7
Fix test.m.wikipedia.org

srv193 doesn't listen on port 81, manually define the backend instead of
trying to do it the structured right way.

Change-Id: I613cff2d66443ce6108080e93bc2ff38c7fbeccd
Merge "Fix failing Nagios check for Parsoid Varnish" into production