Add rax_network module

Based on the refactor work @sivel is doing, adding a rax_network module
to create/delete networks in the Rackspace Public Cloud.

See: https://github.com/ansible/ansible/issues/4577
Update module based on upstream feedback

- Remove deleted state
- Use dict() instead of raw hash
- Wrap or statements in parens instead of backslash line continuations
- Change instances to networks in module return result
Merge pull request #4603 from claco/rax_network_module

Add rax_network module