Centralize bash-completion in Novaclient

Currently the bash-completion code lives partly in Oslo and partly in
Novaclient which makes it difficult to improve the code as the changes need to
be made to two separate projects.

As there aren't any other clients using bash-completion yet, we should
centralize the code in Novaclient while we improve it, and when the API
stabilizes, move it back *in it's entirety*.

This corresponding patch to centralize the functionality in Novaclient is
here:

    https://review.openstack.org/#/c/101373/

Change-Id: I6b0c5157d40642d871c4bb77deef040a574266a0
Closes-Bug: 1332270
Merge "Centralize bash-completion in Novaclient"