Merge ping-msg-unavailable-page-test [f=1455095] [r=ack,free.ekanayaka,landscape-builder] [a=Björn Tillenius]
Renable the tests for ping and message server 503 pages.
The tests were rewritten not to check for unstyled pages. The old charm
used unstyled 503 pages, but for example staging doesn't. Using styled
503 pages is easiest and is consistent with staging.