feat(circleci): triggers grafana packer after successful build

Only triggers for main grafana repo (not forks) and when the
master branch is built.

circle.yml

@@ -27,3 +27,10 @@ test:
      # js tests
      - ./node_modules/grunt-cli/bin/grunt test
      - npm run coveralls
+
+deployment:
+  master:
+    branch: master
+    owner: grafana
+    commands: 
+      - ./trigger_grafana_packer.sh ${TRIGGER_GRAFANA_PACKER_CIRCLECI_TOKEN}