Fix or skip tests for /config_templates API path

The `/config_templates` API path incorrectly rejects some parameters. Skip some
tests that fail due to this issue. For more information, see:

* https://bugzilla.redhat.com/show_bug.cgi?id=1154156
* http://projects.theforeman.org/issues/7989

The API documentation also states that all POST requests to the
`/config_templates` path should be wrapped in an extra hash. Do so.

These two changes fix a number of failing tests. Updated test results:

    $ nosetests tests/foreman/api/test_multiple_paths.py -m ConfigTemplate
    InsecureRequestWarning)
    .SS..S..SS
    ----------------------------------------------------------------------
    Ran 10 tests in 7.735s

    OK (SKIP=5)