Use sets to diff env vars.

I was trying to preserve the ordering, but we sort all the args
anyway. Using sets and subtracting them performs much better than
list comprehensions.

docker-rerun

 
 def handle_environment(container):
     """Copies the environment (-e/--env) arguments."""
-    container_env = container.info['Config']['Env'] or []
-    image_env = container.image_info['Config']['Env'] or []
-    delta = [e for e in container_env if e not in image_env]
+    container_env = set(container.info['Config']['Env'] or [])
+    image_env = set(container.image_info['Config']['Env'] or [])
+    delta = container_env - image_env
     container.args.extend(['--env=%s' % env for env in delta])
 
 

test.py

     ['docker', 'run', '--name=test123', '-d', 'hello-world:latest'],
     ['docker', 'run', '--name=test123', '-d', 'hello-world', '/hello', 'world...'],
     ['docker', 'run', '--env=PATH=/root', '--env=Z=X', '--name=test123', '-d', 'hello-world'],
-    ['docker', 'run', '--env=FOO=bar baz', '--name=test1234', '-d', 'hello-world'],
+    ['docker', 'run', '--env=FOO=bar baz', '--name=test123', '-d', 'hello-world'],
     ['docker', 'run', '--name=test123', '--restart=always', '-d', 'hello-world'],
     ['docker', 'run', '--name=test123', '--restart=on-failure:10', '-d', 'hello-world'],
     ['docker', 'run', '--name=test123', '--net=host', '-d', 'hello-world'],