feature: add support for deploy from source

[Heather Lanigan]

It would be extremely helpful for the OpenStack Principle layer to include openstack-origin-git to allow for install from git as well as by Ubuntu package. Currently I'm working on a charm where the Ubuntu package is behind the code and I need to install from git until the package is updated.

A good number of the old model charms have both openstack-origin and openstack-origin-git.

[Dmitrii Shcherbakov (dmitriis)]

Need to add openstack-origin-git to the config.yaml:

https://github.com/openstack/charm-layer-openstack-principle/blob/master/config.yaml

  openstack-origin-git:
    default:
    type: string

The following code will be triggered in the charm-helpers as a result:
https://bazaar.launchpad.net/~charm-helpers/charm-helpers/devel/view/head:/charmhelpers/contrib/openstack/utils.py#L741

[James Page (james-page)]

This will also require integration of the deploy from source code into charms.openstack to understand what todo with the option.

FWIW there is always a charm specific element to this - so it will require charm specific support as well as general layer support.