Refactor all API v2 docstrings

As API v1 tests will be rewritten the rafactor could happen when
updating the tests.
Merge pull request #1327 from elyezer/docstring-refactor-api-v2

Refactor all API v2 docstrings
Fix four errors emitted by `sphinx make-docs`
Refactor all CLI docstrings

This will make the CLI docs look much better
Merge pull request #1328 from Ichimonji10/sphinx

Fix four errors emitted by `sphinx make-docs`
Trim down ForemanTask, test ForemanTask API

Remove the custom method `ForemanTask.read`. Make `ForemanTask` inherit from
`EntityReadMixin`. `ForemanTask.read_json` performs the same task that the old
`ForemanTask.read` method did, and no code was using the old method.

Add a test targeting bugzilla bug 1131702. The test asserts that when a
non-existent foreman task is read, an HTTP 4XX or 5XX error is received. The
test fails, so it is skipped appropriately.

Add this new test module to the API docs.
Merge pull request #1326 from Ichimonji10/bz-1131702

Trim down ForemanTask, test ForemanTask API
Merge pull request #1329 from elyezer/docstring-refactor-cli

Refactor all CLI docstrings