updated most of Rsync with server-specific auth

As it was, the Rsync module/command was taking most of its config directly from Rex::Config, when get_current_connection->{server} is a Rex::Group::Entry::Server that has proxy methods for most of what it was using, so now it supports group-specific/server-specific auth for the most part.
Merge remote-tracking branch 'tianon/patch-2' into 0.42