Cleanup of dockerfiles, compose files and env vars

Signed-off-by: Christopher Petito <chrisjpetito@gmail.com>

e2e/compose-env.yaml

@@ -1,9 +1,10 @@
 services:
+
   registry:
     image: 'registry:2'
 
   engine:
-      image: 'docker:${TEST_ENGINE_VERSION:-stable-dind}'
+      image: 'docker:${ENGINE_VERSION:-25.0}-dind'
       privileged: true
       command: ['--insecure-registry=registry:5000']
       environment:
@@ -16,6 +17,7 @@ services:
       ports:
         - 4443:4443
       command: ['notary-server', '-config=/fixtures/notary-config.json']
+
   evil-notary-server:
       build:
         context: ./testdata