Improve robustness of client tests

All tests that were failing in CI with this diffs showing traces with
context, which correspond to a default `VERBOSITY verbose` in the server.

Since we migrated the CI to postgres 9.6 it makes sense to see such
differences in server configuration.

Enforcing the verbosity level makes the tests more robust indeed.

client/test/sql/999_permissions_test.sql

@@ -1,3 +1,4 @@
+\set VERBOSITY terse
 -- Use regular user role
 SET ROLE test_regular_user;