Force mod_proxy to immediately close a connection to the backend
after being used, and thus, disable its persistent connection and
pool for that backend.
Let's see if that helps fixing bug #1630664 (the
Connection aborted/ BadStatusLine thing).
We already have an ER query (in queries/1630664.yaml) that should show
whether this is effective.
Change-Id: I03b09f7df5c6e134ec4091a2f8dfe8ef614d1951