Build system: Introduce promu to prometheus-operator

Add 'promu.yml' and 'VERSION' file and replace build recipe to use
promu.

.promu.yml

@@ -0,0 +1,36 @@
+repository:
+    path: github.com/coreos/prometheus-operator
+build:
+    flags: -a -tags netgo
+    binaries:
+        - name: operator
+          path: ./cmd/operator
+tarball:
+    files:
+        - LICENSE
+        - NOTICE
+crossbuild:
+    platforms:
+        - linux/amd64
+        #- linux/386
+        #- darwin/amd64
+        #- darwin/386
+        #- windows/amd64
+        #- windows/386
+        #- freebsd/amd64
+        #- freebsd/386
+        #- openbsd/amd64
+        #- openbsd/386
+        #- netbsd/amd64
+        #- netbsd/386
+        #- dragonfly/amd64
+        #- linux/arm
+        #- linux/arm64
+        #- freebsd/arm
+        #- openbsd/arm
+        #- linux/mips64
+        #- linux/mips64le
+        #- netbsd/arm
+        #- linux/ppc64
+        #- linux/ppc64le
+

Makefile

@@ -2,14 +2,17 @@ REPO?=quay.io/coreos/prometheus-operator
 TAG?=$(shell git rev-parse --short HEAD)
 NAMESPACE?=prometheus-operator-e2e-tests-$(shell LC_CTYPE=C tr -dc a-z0-9 < /dev/urandom | head -c 13 ; echo '')
 
+PROMU := $(GOPATH)/bin/promu
+PREFIX ?= $(shell pwd)
+
 CLUSTER_IP?=$(shell minikube ip)
 
 pkgs = $(shell go list ./... | grep -v /vendor/ | grep -v /test/)
 
 all: check-license format build test
 
-build:
-	go build github.com/coreos/prometheus-operator/cmd/operator
+build: promu
+	@$(PROMU) build --prefix $(PREFIX)
 
 test:
 	@go test -short $(pkgs)
@@ -38,4 +41,9 @@ clean-e2e:
 	kubectl -n $(NAMESPACE) delete prometheus,alertmanager,servicemonitor,statefulsets,deploy,svc,endpoints,pods,cm --all
 	kubectl delete namespace $(NAMESPACE)
 
+promu:
+	@GOOS=$(shell uname -s | tr A-Z a-z) \
+	GOARCH=$(subst x86_64,amd64,$(patsubst i%86,386,$(shell uname -m))) \
+	go get -u github.com/prometheus/promu
+
 .PHONY: all build test format check-license container e2e-test e2e-status e2e clean-e2e

VERSION

@@ -0,0 +1,2 @@
+0.2.3
+