[gke.py] Add initial "gke.py" GKE management tool.
[gke.py] Add initial "gke.py" GKE management tool.

Add "gke.py", a utility to manage Google Container Engine instances.
This will be used by LogDog initially to integrate GKE management into
its Makefile.

"gke.py" is mostly a starting point. It currently implements a single
command, "kubectl", which is a raw portal to the "kubectl" command.

TBR=vadimsh@chromium.org
BUG=None
TEST=local
R=40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org, vadimsh@chromium.org

Change-Id: I6a9a27d51d397df1ec5eda0935f7df2e934dd39a
Reviewed-on: https://chromium-review.googlesource.com/624897
Commit-Queue: Daniel Jacques <8400006a9338a0893dca0101ad49838955bd6b2c@chromium.org>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py