Trim down test_multiple_paths.py

Make all all tested entities (i.e. classes in entities.py) inherit from
`EntityReadMixin`. Take advantage of this fact to trim down module
`test_multiple_paths`.

Add a logger to module `test_multiple_paths`. Log out information in several
tests, thus allowing the assertions to be trimmed down.
Add method `EntityReadMixin.read_raw`

`read_raw` makes a call to the server being tested and returns a
`requests.models.Response` object. It does not perform any validation, such as
checking the HTTP response code or decoding JSON.

Make `EntityReadMixin.read_json` call `EntityReadMixin.read_json`.
Remove 404 handling logic from `EntityReadMixin.read_json` and add this logic to
class `ActivationKey`. The 404 handling logic is only relevant to activation
keys.

Make module `test_multiple_paths` call `read_raw` instead of directly calling
`robottelo.api.client`.

Conflicts:
	robottelo/entities.py
	robottelo/orm.py
	tests/foreman/api/test_multiple_paths.py
Merge pull request #1684 from Ichimonji10/ak-404

Activation Key 404s