Bug 1100905 — Remove redis keys wildcard lookups.
@mikedeboer review.
Rename redis "roomparticipant" to "roomparticipants".

In addition to being cleaner, this will help have two different namespaces for
the participants lists (one for 0.13.2 and one for after).
Merge pull request #254 from mozilla-services/1100905-participant-redis-hashes

Bug 1100905 — Remove redis keys wildcard lookups.