Skip tests failing due to BZ 1154156

The `/users` and `/hosts` paths incorrectly reject parameters that they should
accept. Skip 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

Updated test results:

    $ nosetests tests/foreman/api/test_multiple_paths.py -m User
    .SS..S..SS
    ----------------------------------------------------------------------
    Ran 10 tests in 19.046s

    OK (SKIP=5)