Handle SQL API errors by logging them and requesting NO cache

SQL api is used to determine the list of source tables affected
by a query. Before this commit, the X-Cache-Channel header set
on sql api error was an arbitrary 'table' string, now the header
is omitted, the error logged and Cache-Control and Pragma headers
are sent as an attempt to request no caching.

The code includes test for this mechanism.

test/support/sql/gadm4.sql

@@ -97,8 +97,6 @@ ALTER TABLE ONLY gadm4
 
 CREATE INDEX bdll25_provincias_4326_2_the_geom_webmercator_idx ON gadm4 USING gist (the_geom_webmercator);
 
--- development_cartodb_user_3 role
-CREATE USER development_cartodb_user_3;
-GRANT ALL ON TABLE gadm4 TO development_cartodb_user_3;
+GRANT ALL ON TABLE gadm4 TO test_cartodb_user_1;
 GRANT SELECT ON TABLE gadm4 TO publicuser;