cleaning up Etcd integration. 

Fixes for:

 https://github.com/lytics/metafora/issues/10 - Adds DeleteTask  and Logging to the Client. 

https://github.com/lytics/metafora/issues/35 -  Watch now picks up work submitted before the watcher was started.

https://github.com/lytics/metafora/issues/40 - The first ever coordinator to join the cluster should establish the etcd schema. 

Adds more testscases, including confirming https://github.com/lytics/metafora/issues/26 is fixed 
Let's just call it `_metafora` and we can store version metadata in it someday to allow nodes to check if they're running against a version of the etcd layout they support.