WIP: 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
s/RegistryPath/ProxySettingsRegistryPath/
(or something else that indicates it has to do with proxy settings)