Update to use go modules (#671)

This includes updates to CI config, vendor files, etc.
I've hard-coded the k8s depedency at 1.13.4 to keep it inline with what
we currently have and to make sure a another run of `go mod tidy`
doesn't accidentally update it to an unexpected version.

Thanks to hectorj2f for carrying this along.

vendor/github.com/grpc-ecosystem/grpc-gateway/utilities/readerfactory.go

@@ -0,0 +1,20 @@
+package utilities
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+)
+
+// IOReaderFactory takes in an io.Reader and returns a function that will allow you to create a new reader that begins
+// at the start of the stream
+func IOReaderFactory(r io.Reader) (func() io.Reader, error) {
+	b, err := ioutil.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+
+	return func() io.Reader {
+		return bytes.NewReader(b)
+	}, nil
+}