Use before_cache instead of after_failure to clean cache

.travis.yml

@@ -14,8 +14,8 @@ before_script:
   - sudo service postgresql stop
 
 # Clean the cache if any step fails.
-after_failure:
+before_cache:
-  - scripts/ci clean
+  - scripts/ci fail-clean
 
 cache:
   timeout: 1000

scripts/ci

@@ -43,6 +43,12 @@ clean_cache() {
     rm "${IMAGE_TAR}"
 }
 
+fail_clean() {
+    if [[ $TRAVIS_TEST_RESULT -ne 0 ]]; then
+        echo "Job failed. Cleaning cache..."
+        clean_cache
+    fi
+}
 
 quay_run() {
     docker run --net=host -e TEST_DATABASE_URI -ti "${IMAGE}:${IMAGE_TAG}" "$@"
@@ -148,6 +154,10 @@ case "$1" in
         postgres
         ;;
 
+    fail-clean)
+        fail_clean
+        ;;
+
     clean)
         clean_cache
         ;;