Use the home_assistant user for most tasks

This updates the formula to use the home_assistant user for tasks like
cloning the git repo and making the virtual environment. This allows
home assistant to perform some tasks it otherwise can't do due to
permission issues, like installing needed python libraries at runtime.

This also allows the ssh identity used for cloning the git repo to be
specified.

Signed-off-by: M. David Bennett <mdavidbennett@syntheticworks.com>

Remove salt-master and reclass dependencies

Change-Id: I5ac7b84915e6d24b18ae7ae25f9b84be5bdcd448

Change-Id: Id792744148af5fd586ec09f0f275d0633978505e

Make server.source variable truly optional.

Add support for custom source and version.