Record the output from loading new revisions to the database

So that it can easily be shown through the web interface. There's two tables
being used. One which temporarily stores the output as it's output while the
job is running, and other which stores the whole log once the job has
finished.

sqitch/verify/load_new_guix_revision_job_logs.sql

@@ -0,0 +1,7 @@
+-- Verify guix-data-service:load_new_guix_revision_job_logs on pg
+
+BEGIN;
+
+-- XXX Add verifications here.
+
+ROLLBACK;