Add goenv script and fix Docker

Dockerfile

 FROM        sdurrheimer/alpine-glibc
 MAINTAINER  The Prometheus Authors <prometheus-developers@googlegroups.com>
 
-WORKDIR /app
-COPY    . /app
+WORKDIR /gopath/src/github.com/prometheus/prometheus
+COPY    . /gopath/src/github.com/prometheus/prometheus
 
-RUN apk add --update -t build-deps git make bash go \
+RUN apk add --update -t build-deps tar openssl git make bash \
+    && source ./scripts/goenv.sh /go /gopath \
     && make build \
     && cp prometheus promtool /bin/ \
     && mkdir -p /etc/prometheus \
     && mv ./documentation/examples/prometheus.yml /etc/prometheus/prometheus.yml \
     && mv ./console_libraries/ ./consoles/ /etc/prometheus/ \
     && apk del --purge build-deps \
-    && rm -rf /app /var/cache/apk/*
+    && rm -rf /go /gopath /var/cache/apk/*
 
 EXPOSE     9090
 VOLUME     [ "/prometheus" ]

README.md

@@ -36,7 +36,7 @@ Debian and RPM packages are being worked on.
 ### Building from source
 
 To build Prometheus from the source code yourself you need to have a working
-go environment with [version 1.5 or greater installed](http://golang.org/doc/install).
+Go environment with [version 1.5 or greater installed](http://golang.org/doc/install).
 
 You can directly use the `go` tool to download and install the `prometheus`
 and `promtool` binaries into your `GOPATH`:
@@ -53,7 +53,7 @@ You can also clone the repository yourself and build using `make`:
     $ make
     $ ./prometheus -config.file=your_config.yml
 
-The makefile provides several targets:
+The Makefile provides several targets:
 
   * *build*: build the `prometheus` and `promtool` binaries
   * *test*: run the tests

scripts/goenv.sh

+# 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.
+
+goroot="$1"
+gopath="$2"
+
+go_version_min="1.5"
+go_version_install="1.5.1"
+
+vernum() {
+	printf "%03d%03d%03d" $(echo "$1" | tr '.' ' ')
+}
+
+if command -v "go" >/dev/null; then
+    go_version=$(go version | sed -e 's/^[^0-9.]*\([0-9.]*\).*/\1/')
+fi
+
+# If we satisfy the version requirement, there is nothing to do. Otherwise
+# proceed downloading and installing a go environment.
+if [ $(vernum ${go_version}) -ge $(vernum ${go_version_min}) ]; then
+	return
+fi
+
+export GOPATH="${gopath}"
+export GOROOT="${goroot}/${go_version_install}"
+
+export PATH="$PATH:$GOROOT/bin"
+
+if [ ! -x "${GOROOT}/bin/go" ]; then
+
+	mkdir -p "${GOROOT}"
+
+	os=$(uname | tr A-Z a-z)
+	arch=$(uname -m | sed -e 's/x86_64/amd64/' | sed -e 's/i.86/386/')
+
+	url="https://golang.org/dl"
+	tarball="go${go_version_install}.${os}-${arch}.tar.gz"
+
+	wget -qO- "${url}/${tarball}" | tar -C "${GOROOT}" --strip 1 -xz
+fi