Makes sure redis is never call with undefined key parameters.
Bug 1100905 — Remove redis keys wildcard lookups.
@mikedeboer review.
Fix filter names for redis.

We were using "val" everywhere which doesn't convey any meaning, we are now
using the type of the list we're manipulating (call, url, room).
Rename the credentials var into metadata on /.
Merge pull request #255 from mozilla-services/better-filter-names

Fix filter names for redis.
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).
Put all the function param checks in one function.

This allows to have all this logic in one place and keep the code cleaner.
Merge with master
Merge pull request #254 from mozilla-services/1100905-participant-redis-hashes

Bug 1100905 — Remove redis keys wildcard lookups.
Merge pull request #256 from mozilla-services/rename-homepage-credentials

Rename the credentials var into metadata on /.
Merge master
Merge pull request #248 from mozilla-services/1090140-redis-undefined

Makes sure redis is never call with undefined key parameters.
Refactoring — Add comments to each redis backend methods.
@ametaireau review.