Merge pull request #27570 from Random-Liu/add-runtime-request-timeout-flag

Automatic merge from submit-queue

Add runtime-request-timeout kubelet flag.

XRef #23563.

Addresses https://github.com/kubernetes/kubernetes/issues/27388#issuecomment-226570083.

Add a new kubelet flag `runtime-request-timeout`, and set to 2 minutes by default.
Now the flag only affects dockertools, rkt may also want to set request timeout according to the flag. @yifan-gu 

This PR also removed the timeout for all long running operations to avoid issues like #27588 and #26122.

@yujuhong @rrati 
/cc @kubernetes/sig-node 

[![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/.github/PULL_REQUEST_TEMPLATE.md?pixel)]()

hack/verify-flags/known-flags.txt

@@ -399,6 +399,7 @@ root-dir
 run-proxy
 runtime-cgroups
 runtime-config
+runtime-request-timeout
 save-config
 scheduler-config
 scheduler-name