Include new modules in API docs

New modules have recently been added. Include them in the API docs.
Fix Sphinx build errors

Silence over 100 errors generated by `sphinx-build` when `make docs` is
executed.
Fix flake8 error
Merge pull request #924 from Ichimonji10/housekeeping

Housekeeping
Create some simple tests for path api/v2/hosts

Implement a few tests which check whether it's possible to GET the path, and add
some partially written tests for doing other things like POSTing and messing
with sub-paths of api/v2/hosts.
Use new `requests` wrapper
Add a new API test

Ensure that a HTTP 401 response is generated when an unauthorized HTTP GET
request is made.
Add a pair of HTTP POST tests for the API

Make minimal use of module robottelo.entities while doing this.