Make it possible to create a user via API

When POSTing to the /users URL, wrap data within an extra hash. This is per the
API document.

    $ python -m unittest tests.foreman.api.test_user
    ....s......s......s.....s......s......s.
    ----------------------------------------------------------------------
    Ran 40 tests in 79.635s

    OK (skipped=6)

Targets #1578.
Merge pull request #1585 from Ichimonji10/create-user

Make it possible to create a user via API
Make Sphinx happy

Do not attempt to auto-generate API docs for the non-existent
`robottelo.api.apicrud` module. Fix a module reference.
Skip known-failing tests

Skip tests that are known to fail due to BZ 1154156.

    $ nosetests tests/foreman/api/test_multiple_paths.py -m _Host
    ..S.S.....S.....SSSS
    ----------------------------------------------------------------------
    Ran 20 tests in 48.694s

    OK (SKIP=7)

Make method `Host.create` subnet a nested hash of parameters, e.g. `{'host':
{...}}`.
Merge pull request #1586 from Ichimonji10/docs

Make Sphinx happy
Merge pull request #1588 from Ichimonji10/create-host

Skip known-failing tests
Make API logging more useful

Make the API client log out a warning whenever an HTTP 4XX or 5XX response is
received. Demote messages detailing the contents of every single request and
response from priority "info" to "debug".
Merge pull request #1589 from Ichimonji10/better-logging

Make API logging more useful