Some of the backends tests are disabled

[thedrow]

Our CI skips the tests for MongoDB, CouchDB, Riak and SQLAlchemy.
We need to enable them back and fix the tests if they fail.

[thedrow]

@ask Have we removed all these results backends? Can we close this issue?

[ask]

I didn't remove the result backends, I only removed the broker transports. We could consider removing some of them, but I don't know which ones, and many of them seem to be working.

[thedrow]

So let's re-enable the tests. I'll take of it this weekend.

[ask]

They're all pretty much enabled now:

MISSING FROM CI REQS:
set([u'extras/auth.txt',
     u'extras/couchbase.txt',
     u'extras/librabbitmq.txt',
     u'extras/pyro.txt',
     u'extras/zeromq.txt',
     u'extras/zookeeper.txt'])