Skip tests due to BZ 1162860

Using a non-admin user to do anything causes an exception to be thrown with the
following error messages:

    {"error": {"message":"LdapError: No such address or other socket error."}}

Skip tests that fail due to this error. Before the change:

    $ nosetests tests/foreman/api/test_permission.py:UserRoleTestCase
    EEEEEEEE
    …

    ----------------------------------------------------------------------
    Ran 8 tests in 38.272s

    FAILED (errors=8)

After the change:

    setests tests/foreman/api/test_permission.py:UserRoleTestCase
    SSSSSSSS
    ----------------------------------------------------------------------
    Ran 8 tests in 16.383s

    OK (SKIP=8)