Prior to this change, configure.sh would:
(1) compare versions of built-in kubelet and downloaded kubelet, and
(2) bind-mount downloaded kubelet at /usr/bin/kubelet in case of
version mismatch

With this change, configure.sh:
(1) compares the two versions only on test clusters, and
(2) uses the actual file paths to start kubelet w/o any bind-mounting

To allow (2), this change also provides its own version of kubelet
systemd service file.

Effectively with this change we will always use the downloaded kubelet
binary along with its own systemd service file on non-test clusters.  The
main advantage is this change does not rely on the kubelet being built in to
the OS image.