This change refactors the code of preparing kube-system manifests
for trusty based cluster. The manifests used by nodes do not contain
salt configuration, so we can simply copy them from the directory
cluster/saltbase/salt, make a tarball, and upload to Google Storage.
The node.yaml has some logic that will be also used by the kubernetes
master on trusty work (issue #16702). This change moves the code
shared by the master and node configuration to a separate script, and
the master and node configuration can source it to use the code.
Moreover, this change stages the script for GKE use.
Andy Zheng