Run integration tests with a different stdout_callback

Hopefully this will make errors a bit more readable in CI logs.

test-driver

@@ -113,6 +113,9 @@ case "$cmd" in
         ;;
 
     run)
+        # The 'yaml' output format has slightly more legible errors.
+        export ANSIBLE_STDOUT_CALLBACK=yaml
+
         for playbook in "${float_dir}/test/integration-test-docker.yml" "$@"; do
             log Running test playbook ${playbook}
             ${float_dir}/float run ${playbook} \