Dev mode doesn't always work

[Mark Goddard]

The kolla-ansible dev mode currently works by bind mounting in a source code repo under site-packages/<python>/<package> in the virtualenv in the container. This might not work in several cases:

* If there are new files in the source, these will not be present in the package file manifest. I think you can still import those python files, but they will not appear if you inspect the package, e.g. to find entry points.
* Similar to above but for removed files.
* Files installed outside of the python package directory are unaffected, e.g. bin/, share/, data_files, etc.

A better approach would be to bind mount the source code under e.g. /src/<repo>, then modify kolla to pip install any packages found in that directory on startup.