[FLOC-4513] Use upstream mimic package

[wallrj]

Fixes: https://clusterhq.atlassian.net/browse/FLOC-4513

Mimic 2.2.0 was released so we no longer have to install from a ClusterHQ fork:

• https://github.com/rackerlabs/mimic/pull/705

A bunch of other requirements got updated at the same time.

[wallrj]

The four failing acceptance tests are failing on master too so I'm going to merge anyway.

• http://ci-live.clusterhq.com:8080/job/ClusterHQ-flocker/view/master/job/master/view/cron/