Support builds on macOS

The BSD version of sed does not support multiple `-e` flags and
`sha256sum` is not installed by default. This commit makes minor changes
to ensure a macOS user may build agones without any additional effort.

build/Makefile

@@ -55,7 +55,13 @@ common_mounts = -v $(build_path)/.config/gcloud:/root/.config/gcloud \
 
 # Use a hash of the Dockerfile for the tag, so when the Dockerfile changes,
 # it automatically rebuilds
-build_version := $(shell sha256sum $(build_path)/build-image/Dockerfile | head -c 10)
+build_version := $(shell \
+	if hash sha256sum 2>/dev/null; then \
+		sha256sum $(build_path)/build-image/Dockerfile | head -c 10; \
+	else \
+		shasum -a 256 $(build_path)/build-image/Dockerfile | head -c 10; \
+	fi \
+)
 build_tag = agones-build:$(build_version)
 build_remote_tag = $(REGISTRY)/$(build_tag)
 controller_tag = $(REGISTRY)/agones-controller:$(VERSION)
@@ -109,9 +115,10 @@ install: ALWAYS_PULL_SIDECAR := true
 install: IMAGE_PULL_POLICY := "Always"
 install: ensure-build-image
 	cp $(build_path)/install.yaml $(build_path)/.install.yaml
-	sed -i -e 's!$${REGISTRY}!$(REGISTRY)!g' -e 's!$${VERSION}!$(VERSION)!g' \
-		-e 's!$${IMAGE_PULL_POLICY}!$(IMAGE_PULL_POLICY)!g' -e 's!$${ALWAYS_PULL_SIDECAR}!$(ALWAYS_PULL_SIDECAR)!g' \
-		$(build_path)/.install.yaml
+	sed -i -e 's!$${REGISTRY}!$(REGISTRY)!g' $(build_path)/.install.yaml
+	sed -i -e 's!$${VERSION}!$(VERSION)!g' $(build_path)/.install.yaml
+	sed -i -e 's!$${IMAGE_PULL_POLICY}!$(IMAGE_PULL_POLICY)!g' $(build_path)/.install.yaml
+	sed -i -e 's!$${ALWAYS_PULL_SIDECAR}!$(ALWAYS_PULL_SIDECAR)!g' $(build_path)/.install.yaml
 	docker run --rm $(common_mounts) $(ARGS) $(build_tag) kubectl apply -f $(mount_path)/build/.install.yaml
 
 # Build a static binary for the gameserver controller
@@ -287,4 +294,4 @@ minikube-install: minikube-agones-profile
 # Convenience target for transferring images into minikube.
 # Use TAG to specify the image to transfer into minikube
 minikube-transfer-image:
-	docker save $(TAG) | ($(MINIKUBE_DOCKER_ENV) && docker load)
+	docker save $(TAG) | ($(MINIKUBE_DOCKER_ENV) && docker load)