DO NOT MERGE - REVIEW ONLY require username and password for swarm create

[vieux]

Close #695

The server side part, isn't live yet please review the code.

Added a -u,--username and -p.--password to swarm create
Alternatively you can do a swarm create and it will ask for the username and password (without echo, like docker login)

You can combine with:

$ swarm create -u vieux
Password:

53128764320641268482352786912

[vieux]

ping @abronan @aluzzardi @jlhawn

[vieux]

I know the tests are broken, I did it on purpose so we don't merge.

[aluzzardi]

As discussed IRL, how about having destroy as well, requiring the same auth (both client and server side)

[aluzzardi]

Also, this set aside, how about moving from discovery-staging to discovery?

[vieux]

I agree on the destroy but let's change the url in another PR

[aluzzardi]

How about this workflow:

$ swarm create
Warning: Anonymous cluster created. Anonymous clusters can be destroyed by anyone with knowledge of the token. Please provide a `--username` in order to create an authenticated cluster.
53128764320641268482352786912

$ swarm create -u vieux
Password:
53128764320641268482352786912

/cc @bfirsh @shykes

[vieux]

ping @bfirsh @shykes

[moxiegirl]

@vieux Do we need to update the user-facing documentation for this? I saw you hit the token README