Set kubelet user home directory to /var/lib/kubelet

The kubelet user does not have permissions to create directories in
/var/lib. This sets the home directory to /var/lib/kubelet so that the
directory is made prior to running the kubelet. This matches the
default root directory path (/var/lib/kubelet) and allows kubelet to
us that directory.
Merge pull request #689 from Sarsate/salt-kubelet-dir

Set kubelet user home directory to /var/lib/kubelet