This fix uses docker container for kubectl. Since Kubernetes docker
image hyperkube has already been downloaded and it consists of
kubectl, there is really no need to download kubectl binary again.
This fix cleans up the Kubernetes related travis setup and removes
unneeded scripts.
This fix also fixes several mismatches of the Kubernetes version used,
so that any changes in version in the future only need to update .travis.yml.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
