Support an optional APP_TAG envvar. Apps would typically use this to assign a tag to gcr.io/deustis-test-2/wordpress/test-01 images. Also modifies  path.
Support an optional APP_TAG envvar. Apps would typically use this to assign a tag to gcr.io/deustis-test-2/wordpress/test-01 images. Also modifies  path.

cliveseldon/marketplace-k8s-app-tools,GoogleCloudPlatform/marketplace-k8s-app-tools,cliveseldon/marketplace-k8s-app-tools,GoogleCloudPlatform/marketplace-k8s-app-tools,cliveseldon/marketplace-k8s-app-tools,janetkuo/marketplace-k8s-app-tools,janetkuo/marketplace-k8s-app-tools,cliveseldon/marketplace-k8s-app-tools