allow more use cases use of hiera

Useability improvement: this allows to return easier types when possible by the query.  I use it with a .sql file like this:

parameters: SELECT name,data FROM parameters WHERE node='%{::fqdn}' OR node='%{hostname}' OR node='*' ; 
classes: SELECT classname AS classes FROM classes WHERE node='%{::fqdn}' OR node='%{hostname}' OR node='*';
default_query: SELECT data FROM parameters WHERE (node='%{::fqdn}' OR node='%{hostname}' OR node='*') AND name='%{key}';

This in turn allows me to do things like hiera_include("classes",'') and use the backend to drive stuff like class repmgr ($nodeid = '') where the nodeid comes right out of hiera-postgres-backend.