[LIBCLOUD-577] Add an example to OpenStack driver documentation which shows how
to specify a tenant name.
Sort the regions for a consistent result.
Re-generate supported methods file.
Add initial implementation of a base networking API with a reference drivers
for OpenStack Neutron and OpenStack Quantum.

Also add support for retrieving a networking driver to the OpenStack compute
driver.

Note: Base API hasn't been decided upon yet and is subject to change.
Merge branch 'base_networking_api' of https://github.com/Kami/libcloud into base_networking_api