Add version to 'auth' component, send it to auth-service

Now that swarming components are starting to be used in other GAE apps, it 
makes difficult to keep track and control what revision exactly is used 
everywhere. It is particularly important for 'auth' component because it 
communicates with central auth-service. If we add some new features to 
auth-serice we'd like to be sure that all linked services know how to use them.

I propose:
1) Add components/auth/version.py file that defines __version__ of auth module 
(e.g. '1.0'). It is a separate file for easier 'git log' queries.
2) __version__ is bumped on changes to auth component API or feature set.
3) Expose __version__ in Primary <-> Replicate protocol.
4) Show __version__ of replicas in Primary UI.

That way if some linked service is running old auth code we'd at least know 
about it.

Original issue reported on code.google.com by vadimsh@chromium.org on 12 Dec 2014 at 10:33

madecoste / swarming

Add version to 'auth' component, send it to auth-service #190