Instead of downloading kubernetes.tar.xz for extracting "kubectl"
binary, we should download only kubectl binary(v1.2.0) for accessing
kubernetes cluster.
Reason for this change: The tar archive is of
large size(above 100MB for v1.0.1 and above 400MB for v1.2.0) which
is not required.
Closes-Bug: #1656752
Change-Id: I6c0013c6900252486129a9ba0e7d9df23d577d77