(PUP-2290) Issue warning when rest/find results in 404

This makes the indirector for rest.find issue a warning when
the server returns a 404. The warning is issued once.

The intent of this is to give the user more feedback about the cause of
a "not found", typically when using a non existing environment. If no
warning is given no clue is presented except an info level log item on
the master side.
(PUP-2290) Fix typo - 400 should be 404
(PUP-2290) Add a spec test for the issued warning for find 404 in REST
Merge pull request #2597 from hlindberg/pup-2290_warn-cause-of-cert-not-found

(PUP-2290) Issue warning when rest/find results in 404