prompts for passwords instead of setting them on the invocation

Feanil/proper extra vars

This seperates the git refs from the rest of the vars because the git refs should end up in
the ami document in mongo but the other vars should not.

E0d/commoncluster

change to chmod as privileged user.

adding EDXAPP_LOCAL_GIT_IDENTITY to abbey.py

also adds some clarifying comments

E0d/es cluster

edxapp-git-auth: allow authenticated edx-platform/edx-theme checkouts

Using `EDXAPP_LOCAL_GIT_IDENTITY` gives parsing errors during evaluation for paths

Setting default username to root and defalut db name to edxapp.

Change how abby gets notified.

We were previously using the jenkins api which was more complicated than the
buildByTokens plugin and its API.

Jarv/focaccia