Align watch_data_get_all with other "all" methods, and
return all watch data without requiring an ID. We may
also need by_id and by_name variants but this is more
consistent and makes things easier for cloudwatch.
Change-Id: I09c90278349efc769ab7c719f686a1fd854b425a
Signed-off-by: Steven Hardy <shardy@redhat.com>