hack: Switch some $(dirname $0)../blah to use ${KUBE_*} vars

This doesn't fix anything broken. But we have config-go which exports
KUBE_REPO_ROOT and KUBE_TARGET.  Using those means the test scripts can
be more easily moved around the repo and still work.  Especially in
hack/test-integration.sh where we use hack/build-go.sh which is going
to use KUBE_TARGET to place the binary, then we use a different method
to find/execute the binary...

If the $(dirname $0)/../ method is prefered to sourcing config-go, feel free to just close this...