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` submit a nested hash of parameters, e.g. `{'host':
{...}}`.