Updates from CAPI PR

- Switch to v1alpha4
- Use more of the CAPD Makefile

Dockerfile

@@ -1,7 +1,29 @@
+# syntax=docker/dockerfile:experimental
+
+# Copyright 2020 The Kubernetes Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
 # Build the manager binary
-FROM golang:1.13 as builder
+FROM golang:1.15 as builder
 
 WORKDIR /workspace
+
+# Run this with docker build --build_arg goproxy=$(go env GOPROXY) to override the goproxy
+ARG goproxy=https://proxy.golang.org
+# Run this with docker build --build_arg package=./controlplane/kubeadm or --build_arg package=./bootstrap/kubeadm
+ENV GOPROXY=$goproxy
+
 # Copy the Go Modules manifests
 COPY go.mod go.mod
 COPY go.sum go.sum