[build] Add gofmt-related Makefile targets

This adds `verify-gofmt` and `gofmt` make targets for quick go-fmting.
It also adds a `verify` target which verifies `gofmt` and the runs the
unit tests.

Travis now runs `make verify` instead of just `make test` as the tests.

hack/gofmt-all.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+
+# Copyright 2017 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.
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+verify=0
+if [[ ${1:-} = "--verify" || ${1:-} = "-v" ]]; then
+  verify=1
+fi
+
+find_files() {
+  find . -not \( \( \
+    -wholename './_output' \
+    -o -wholename './vendor' \
+  \) -prune \) -name '*.go'
+}
+
+if [[ $verify -eq 1 ]]; then
+  diff=$(find_files | xargs gofmt -s -d 2>&1)
+  if [[ -n "${diff}" ]]; then
+    echo "gofmt -s -w $(echo "${diff}" | awk '/^diff / { print $2 }' | tr '\n' ' ')"
+    exit 1
+  fi
+else
+  find_files | xargs gofmt -s -w
+fi