add helper script to upgrade k8s

- added helper script
  from https://github.com/kubernetes/kubernetes/issues/79384#issuecomment-521493597
  to scripts/upgrade-k8s.sh

- removed bashisms from the script

Signed-off-by: Ed Bartosh <eduard.bartosh@intel.com>

scripts/upgrade-k8s.sh

@@ -0,0 +1,24 @@
+#!/bin/sh -eu
+
+# based on the work discussed in
+# https://github.com/kubernetes/kubernetes/issues/79384#issuecomment-521493597
+
+if [ $# != 1 ] || [ "$1" = "?" ] || [ "$1" = "--help" ]; then
+    echo "Usage: $0 <k8s version>" >&2
+    exit 1
+fi
+
+VERSION="$1"
+
+for MOD in $(
+    curl -sS https://raw.githubusercontent.com/kubernetes/kubernetes/v${VERSION}/go.mod |
+    sed -n 's|.*k8s.io/\(.*\) => ./staging/src/k8s.io/.*|k8s.io/\1|p'
+); do
+    echo "$MOD"
+    V=$(
+        go mod download -json "${MOD}@kubernetes-${VERSION}" |
+        sed -n 's|.*"Version": "\(.*\)".*|\1|p'
+    )
+    go mod edit "-replace=${MOD}=${MOD}@${V}"
+done
+go get "k8s.io/kubernetes@v${VERSION}"