Switching exit policy's can_exit_to() and is_match() be permissive

Switching how the ExitPolicy's can_exit_to() and ExitPolicyRule's is_match()
handle an undefined address or port. Previously we reported if we matched or
allowed exiting to *all* instance of the defined destination. Now, however,
rather if we match against *any*.

Change was requested by Aaron Johnson. You can still get the old behavior by
setting the 'strict' argument.