Move update-generated-runtime into common script

Now update-generated-proto-bindings rules all the api.pb.go generation.

Running this shows no delta on the runtime.pb.go

This exposes an issue in how protoc is called for protos that specify
`go_package` which is fixed here.

Not all of our protos specify that option (even though it is
recommended), which will be fixed subsequently.

hack/lib/protoc.sh

@@ -56,10 +56,19 @@ function kube::protoc::protoc() {
   local package=${1}
   gogopath=$(dirname "$(kube::util::find-binary "protoc-gen-gogo")")
 
-  PATH="${gogopath}:${PATH}" protoc \
-    --proto_path="${package}" \
-    --proto_path="${KUBE_ROOT}/vendor" \
-    --gogo_out=plugins=grpc:"${package}" "${package}/api.proto"
+  (
+    cd "${package}"
+
+    # This invocation of --gogo_out produces its output in the current
+    # directory (despite gogo docs saying it would be source-relative, it
+    # isn't).  The inputs to this function do not all have a common root, so
+    # this works best for all inputs.
+    PATH="${gogopath}:${PATH}" protoc \
+      --proto_path="${package}" \
+      --proto_path="${KUBE_ROOT}/vendor" \
+      --gogo_out=paths=source_relative,plugins=grpc:. \
+      api.proto
+  )
 }
 
 # Formats $1/api.pb.go, adds the boilerplate comments and run gofmt on it