ci: do not silently fail

Rationale:
    31722a2 changed the CI scripts to
    not output messages to the logs unless an err occurs to prevent
    exceeding CI runner log limits. A wrong assumption made by that
    commit causes the CI to not output the messages even if there's an
    error. This commit fixes that.

ci/test_run_all.sh

@@ -6,9 +6,14 @@
 
 export LC_ALL=C.UTF-8
 
+# latest_stage.log will contain logs for a silenced stage if it
+# fails.
+trap "cat latest_stage.log" EXIT
+
 set -o errexit; source ./ci/test/00_setup_env.sh
 set -o errexit; source ./ci/test/03_before_install.sh
-set -o errexit; source ./ci/test/04_install.sh &> 04.log || (cat 04.log && exit 1)
-set -o errexit; source ./ci/test/05_before_script.sh &> 05.log || (cat 05.log && exit 1)
+set -o errexit; source ./ci/test/04_install.sh &> latest_stage.log
+set -o errexit; source ./ci/test/05_before_script.sh &> latest_stage.log
+echo -n > latest_stage.log
 set -o errexit; source ./ci/test/06_script_a.sh
 set -o errexit; source ./ci/test/06_script_b.sh