Deactivate workers for windows

Authenticationworker and rsyslog workers are not supported on windows yet. The authentication worker will be ported on windows to add support for winrm. Rsyslog is not supported on windows yet.

This pull request depends on https://github.com/juju/juju/pull/244
Not a fan of throwing away the error here.  We should probably just panic if the current series is somehow not an OS we understand.... it should never happen, but at least if we panic, we'll know if it does.