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 
Technically using Set could put the wrong information in the file if another node beat this node to creating it, but whatever. It's harmless.