The health check requests from haproxy cause uwsgi to write a
lot of useless log lines. This can make it more difficult to find
a problem with a particular service.
This patch adds a route to look for the `osa-haproxy-healthcheck`
user agent string, which haproxy uses when performing health checks.
Any requests with that user agent are not logged.
Closes-Bug: 1742718
Change-Id: Ia163d1686274bd3b80a046a945fb7d7ceb5f721c
(cherry picked from commit 943b5c560b)
48019740f8