oo-diagnostics: test_mcollective_direct_addressing

Add `test_mcollective_direct_addressing`, which checks that `direct_addressing` is disabled in MCollective's `client.cfg` (on broker hosts) and `server.cfg` (on node hosts).

This commit fixes bug 1144615.
This check is not strictly needed because `cfgfiles.each` will evaluate to `[].each` (i.e., a no-op) if `@is_broker` and `@is_node` are both false.  I can remove this check if that would be clearer.