use prometheus common makefile for building

Makefile

+VERSION := 0.0.1
+TARGET := rsyslog_exporter
+GOFLAGS := -ldflags "-X main.Version $(VERSION)"
+
+include Makefile.COMMON

Makefile.COMMON

+# Copyright 2015 The Prometheus 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.
+
+# THE AUTHORITATIVE VERSION OF THIS MAKEFILE LIVES IN:
+#
+#   https://github.com/prometheus/utils
+#
+# PLEASE MAKE ANY CHANGES THERE AND PROPAGATE THEM TO ALL PROMETHEUS
+# REPOSITORIES THAT ARE USING THIS MAKEFILE.
+#
+# This file provides common Makefile infrastructure for several Prometheus
+# components. This includes make tasks for downloading Go, setting up a
+# self-contained build environment, fetching Go dependencies, building
+# binaries, running tests, and doing release management. This file is intended
+# to be included from a project's Makefile, which needs to define the following
+# variables, at a minimum:
+#
+# * VERSION - The current version of the project in question.
+# * TARGET  - The desired name of the built binary.
+#
+# Many of the variables defined below are defined conditionally (using '?'),
+# which allows the project's main Makefile to override any of these settings, if
+# needed. See also:
+#
+# https://www.gnu.org/software/make/manual/html_node/Flavors.html#Flavors.
+#
+# The including Makefile may define any number of extra targets that are
+# specific to that project.
+
+VERSION ?= $(error VERSION not set in including Makefile)
+TARGET  ?= $(error TARGET not set in including Makefile)
+
+SRC    ?= $(shell find . -type f -name "*.go" ! -path "./.build/*")
+GOOS   ?= $(shell uname | tr A-Z a-z)
+GOARCH ?= $(subst x86_64,amd64,$(patsubst i%86,386,$(shell uname -m)))
+
+ifeq ($(GOOS),darwin)
+	RELEASE_SUFFIX ?= -osx$(shell sw_vers -productVersion)
+endif
+
+GO_VERSION ?= 1.4.2
+GOURL      ?= https://golang.org/dl
+GOPKG      ?= go$(GO_VERSION).$(GOOS)-$(GOARCH)$(RELEASE_SUFFIX).tar.gz
+GOPATH     := $(CURDIR)/.build/gopath
+
+# Check for the correct version of go in the path. If we find it, use it.
+# Otherwise, prepare to build go locally.
+ifeq ($(shell command -v "go" >/dev/null && go version | sed -e 's/^[^0-9.]*\([0-9.]*\).*/\1/'), $(GO_VERSION))
+	GOCC   ?= $(shell command -v "go")
+	GOFMT  ?= $(shell command -v "gofmt")
+	GO     ?= GOPATH=$(GOPATH) $(GOCC)
+else
+	GOROOT ?= $(CURDIR)/.build/go$(GO_VERSION)
+	GOCC   ?= $(GOROOT)/bin/go
+	GOFMT  ?= $(GOROOT)/bin/gofmt
+	GO     ?= GOROOT=$(GOROOT) GOPATH=$(GOPATH) $(GOCC)
+endif
+
+# Never honor GOBIN, should it be set at all.
+unexport GOBIN
+
+SUFFIX   ?= $(GOOS)-$(GOARCH)
+BINARY   ?= $(TARGET)
+ARCHIVE  ?= $(TARGET)-$(VERSION).$(SUFFIX).tar.gz
+ROOTPKG  ?= github.com/digitalocean/$(TARGET)
+SELFLINK ?= $(GOPATH)/src/$(ROOTPKG)
+
+default: $(BINARY)
+
+$(GOCC):
+	@echo Go version $(GO_VERSION) required but not found in PATH.
+	@echo About to download and install go$(GO_VERSION) to $(GOROOT)
+	@echo Abort now if you want to manually install it system-wide instead.
+	@echo
+	@sleep 5
+	mkdir -p $(GOROOT)
+	curl -L $(GOURL)/$(GOPKG) | tar -C $(GOROOT) --strip 1 -xz
+
+$(SELFLINK):
+	mkdir -p $(dir $@)
+	ln -s $(CURDIR) $@
+
+dependencies-stamp: $(GOCC) $(SRC) | $(SELFLINK)
+	$(GO) get -d
+	touch $@
+
+$(BINARY): $(GOCC) $(SRC) dependencies-stamp Makefile Makefile.COMMON
+	$(GO) build $(GOFLAGS) -o $@
+
+.PHONY: archive
+archive: $(ARCHIVE)
+
+$(ARCHIVE): $(BINARY)
+	tar -owner=root --group=root -czf $@ $<
+
+.PHONY: tag
+tag:
+	git tag $(VERSION)
+	git push --tags
+
+.PHONY: test
+test: $(GOCC) dependencies-stamp
+	$(GO) test ./...
+
+.PHONY: format
+format: $(GOCC)
+	find . -iname '*.go' | egrep -v "^\./\.build|./generated|\./Godeps|\.(l|y)\.go" | xargs -n1 $(GOFMT) -w -s=true
+
+.PHONY: clean
+clean:
+	rm -rf $(BINARY) $(ARCHIVE) .build *-stamp