Deprecate the `server` option (if we decide to actually deprecate it)

Deprecate the `server` option in favor of the new `server_urls` option. Note that this is still under discussion.

We need to consider how this will interact with the `server_urls` option is also specified.

We should also consult with UX / CS about the impact this will have. Using --server seems like a very common workflow and we probably don't want to disrupt it if not completely necessary.

If we decide to move forward with the deprecation, a number of puppet acceptance tests will need to be updated, as many use -server in conjunction with the -test option currently.