Cleanup how variables are specified and loaded:

Cleanup how variables are specified and loaded:
- define more common variables in share/common
- cleanup how defaults are specified
- fix how CHECK_KEYSERVER was determined in monkeysphere

Fix calls to update_known_hosts and update_authorized_keys in
monkeysphere so that some of the checks are done within the functions
themselves, as opposed in the monkeysphere wrapper, so that other
functions can call them easier.

Fix ssh-proxycommand that had some left over cruft from the
transition.