Fully qualify table names on trigger invalidation caches

[zenitraM]

Right now, as we generate the invalidation tags based on CDB_QueryTablesText output, we tag tables with:
schemaname.tablename
even if the schema name could be omitted. This is because CDB_QueryTables formats it explicitly:
https://github.com/CartoDB/cartodb-postgresql/blob/master/scripts-available/CDB_QueryTables.sql#L48+

However, when we call cdb_invalidate_varnish, we pass it a casted to text regclass, which might only be tablename if schemaname is first on the search path.

This works de chiripa as our regex is permissive enough on upper layers to invalidate X-Cache-Channel for schemaname.tablename when tablename is sent, but might break any invalidations which need strict matches such as Surrogate-Key's.