fix: make deploy.kind didn't work, anymore.

After kubernetes-retired#1306 has been
merged, `make deploy.kind` broke because it doesn't provide the
`KIND_CLUSTER_NAME` variable. An empty default provided to `kind`'s
`--name` parameter doesn't make much sense because `kind` will simply
error out in that case so using a default of `kind` for the name is
the solution that should work most of the time, especially when
following the quick start guide in the README.md.

scripts/deploy-kubefed.sh

@@ -162,7 +162,7 @@ fi
 # Use KIND_LOAD_IMAGE=y ./scripts/deploy-kubefed.sh <image> to load
 # the built docker image into kind before deploying.
 if [[ "${KIND_LOAD_IMAGE:-}" == "y" ]]; then
-    kind load docker-image "${IMAGE_NAME}" --name="${KIND_CLUSTER_NAME:-}"
+    kind load docker-image "${IMAGE_NAME}" --name="${KIND_CLUSTER_NAME:-kind}"
 fi
 
 cd "$(dirname "$0")/.."