removed /app volume from dockerfile

Specifying a volume at `/app` (in the Dockerfile) makes it difficult to
use this image as a base image for derived images. Due to this, we have
removed the `VOLUME` instruction that mounts `/app` as a volume.

The `/app` path continues to function like it did before. As a result if
you want to mount your php application into the container, mount your
application source at `/app` using `-v
/path/on/application/source:/app`.

bitnami/node/test.sh

@@ -57,13 +57,6 @@ teardown() {
   [ "$status" = 0 ]
 }
 
-@test "all the volumes exposed" {
-  docker inspect $CONTAINER_NAME | {
-    run grep "\"Volumes\":" -A 1
-    [[ "$output" =~ "/app" ]]
-  }
-}
-
 @test "port 3000 exposed" {
   add_app
   docker exec -d $CONTAINER_NAME sh -c 'npm install express && node server.js'