Merge pull request #122 from betatim/one_more_rm

[MRG] Remove intermediate containers for successful and failed builds

repo2docker/detectors.py

@@ -716,6 +716,8 @@ class DockerBuildPack(BuildPack):
                 tag=image_spec,
                 buildargs={},
                 decode=True,
+                forcerm=True,
+                rm=True
         ):
             yield line