Makefile: Use 'git diff' to show gofmt changes

This makes fixing errors easier.  Before this commit, errors looked
like [1]:

  $ make gofmt
  libpod/container_linux.go:1:⚠️ file is not gofmted with -s (gofmt)
  make: *** [gofmt] Error 1

But that's not very helpful when your local gofmt thinks the file is
fine.  With this commit, errors will look like:

  $ make gofmt
  find . -name '*.go' ! -path './vendor/*' -exec gofmt -s -w {} \+
  git diff --exit-code
  diff --git a/libpod/container_internal.go b/libpod/container_internal.go
  index df4de3fe..22b39870 100644
  --- a/libpod/container_internal.go
  +++ b/libpod/container_internal.go
  @@ -1,7 +1,7 @@
   package libpod

   import (
  -"bytes"
  +       "bytes"
          "context"
          "encoding/json"
          "fmt"
  make: *** [Makefile:87: gofmt] Error 1

(or whatever, I just stuffed in a formatting error for demonstration
purposes).

Also remove the helper script in favor of direct Makefile calls,
because with Git handling difference reporting and exit status, this
becomes a simpler check.  find's -exec, !, and -path arguments are
specified in POSIX [2].

[1]: https://travis-ci.org/kubernetes-incubator/cri-o/jobs/331949394#L1075
[2]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/find.html

Signed-off-by: W. Trevor King <wking@tremily.us>

Closes: #1038
Approved by: rhatdan

Makefile

@@ -83,10 +83,8 @@ lint: .gopathok varlink_generate
 	@./.tool/lint
 
 gofmt:
-	@./hack/verify-gofmt.sh
-
-fix_gofmt:
-	@./hack/verify-gofmt.sh -f
+	find . -name '*.go' ! -path './vendor/*' -exec gofmt -s -w {} \+
+	git diff --exit-code
 
 test/bin2img/bin2img: .gopathok $(wildcard test/bin2img/*.go)
 	$(GO) build -ldflags '$(LDFLAGS)' -tags "$(BUILDTAGS) containers_image_ostree_stub" -o $@ $(PROJECT)/test/bin2img

hack/verify-gofmt.sh

@@ -1,39 +0,0 @@
-#!/bin/bash
-
-set -o errexit
-set -o nounset
-set -o pipefail
-
-find_files() {
-  find . -not \( \
-      \( \
-        -wholename '*/vendor/*' \
-      \) -prune \
-    \) -name '*.go' \
-    -not \( -wholename './_output/*' \) \
-    -not \( -wholename './cmd/podman/ioprojectatomicpodman/ioprojectatomicpodman.go' \)
-}
-FIX=0
-GOFMT="gofmt -s"
-bad_files=$(find_files | xargs $GOFMT -l)
-
-while getopts "f?:" opt; do
-    case "$opt" in
-        f) FIX=1
-            ;;
-    esac
-done
-
-if [[ -n "${bad_files}" ]]; then
-    if (($FIX == 1)) ; then
-        echo "Correcting the following files:"
-        echo "${bad_files}"
-        while read -r go_file; do
-            gofmt -s -w $go_file
-        done <<< "${bad_files}"
-    else
-      echo "!!! '$GOFMT' needs to be run on the following files: "
-      echo "${bad_files}"
-      exit 1
-  fi
-fi