Automatic merge from submit-queue

Trusty: Fixes for running GKE master

This PR includes two fixes for running GKE master on our image: 
(1) The kubelet command line assembly had a missing part for cbr0. We did not catch it because the code path is not covered by OSS k8s tests;

(2) Remove the "" from the variables in the cert files. It causes a parsing issue in GKE. Again, this code path is not covered by k8s tests.

This PR also refactors the code for assembling kubelet flag. I move all logic into a single function assemble_kubelet_flags in configure-helper.sh for better readability and also simplify node.yaml and master.yaml. 

@roberthbailey @dchen1107 please review it, and mark it as cherrypick-candidate. This PR is verified by @maisem. Together with his CL for GKE, we can run GKE cluster with master on our image and nodes on ContainerVM.

cc/ @maisem @fabioy @wonderfly FYI