Yolo: adding cargo_home to arti's and copying over run restricts to test-json-api job

.gitlab-ci.yml

@@ -38,6 +38,8 @@ build-json-api:
   artifacts:
     paths: 
       - json-api/target/
+      - $CARGO_HOME
+
     expire_in: 15 mins
 
 
@@ -45,7 +47,12 @@ test-json-api:
   stage: test
   needs: 
     - build-json-api
-  only: [ "master" ]
+  only:
+    refs:
+      - master
+
+    changes:
+      - json-api/
 
   dependencies:
     - build-json-api