Autotest Sphinx-based Documentation infrastructure

It's been a while since we've discussed the current state of
Autotest's documentation. While the content has been updated
frequently via the wiki, the current infrastructure is not ideal.

We evaluated many possibilities and we understood that going with
Sphinx (sphinx-doc.org) is our best option. The idea is to move
all documentation from the wiki to Autotest main repo. Doing this,
we'll have:

* Per branch/release documentation
* Documentation attached to patches that introduce new features

And all the other goodies that Sphinx gives us for free, such as
multiple output support and cross reference with other project's
documentation. This last feature is very important because it will
allow say, virt-test, to have a documentation that references
autotest base libraries very easily. The same thing applies to
applications based on ARC, that use the interface the RPC server
offers.

Besides the infrastruture that this patchset brings, there's also
a first attempt to document the RPC server.

In the near future I hope we'll be able to improve even more the
state of our documentation by using sphinx's extension support.
The first extensions in development to suit our own needs:

* Better auto documentation of Django models
* Auto documentation of optparse.OptionParser instances so that
  we'll have auto-generated man pages.

Please git this a try. You can build the documentation by running:

$ python setup.py build_doc

This will generate the html output on build/sphinx/html.