all: display pool status and delete failed/old pods

* status page shows kube pool details
* pods created by the coorindator are tracked
* pods that fail to create are deleted
* pods older than delete-at are deleted
* pods created by a different coordinator are deleted

Updates golang/go#12546

Change-Id: I4c4f8ff906962b4a014a66d0a9d490ff17710d62
Reviewed-on: https://go-review.googlesource.com/16101
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
6 files changed