leaving enabled for single server sandboxes

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

adds support for from-scratch installs
and leaving services stopped

This modifies the edx_ansible role to dump a clean var
file on disk that can be used for subsequent update runs
so that config vars will not be lost

also changes the ansible tmp directory to /var/tmp which is a better
location than using $HOME (used for debugging mostly)