scheduler: delete containers by name

scheduler.json gets nuked during updates. When the box code restarts,
the scheduler is unable to remove old container because the state file
scheduler.json is now gone. It proceeds to create new container but that
does not work because of name conflict.

Fixes #531

src/docker.js

@@ -17,8 +17,10 @@ exports = module.exports = {
     createContainer: createContainer,
     startContainer: startContainer,
     stopContainer: stopContainer,
+    stopContainerByName: stopContainer,
     stopContainers: stopContainers,
     deleteContainer: deleteContainer,
+    deleteContainerByName: deleteContainer,
     deleteImage: deleteImage,
     deleteContainers: deleteContainers,
     createSubcontainer: createSubcontainer