Merge ~bjornt/maas:release-prepare-fail-if-no-change into maas:master

[Björn Tillenius]

Prevent release-prepare from committing if the version didn't change.

The main reason for this is to prevent it being run by mistake and add
unneeded entries to debian/changelog.

[MAAS Lander (maas-lander)]

UNIT TESTS
-b release-prepare-fail-if-no-change lp:~bjornt/maas/+git/maas into -b master lp:~maas-committers/maas

STATUS: FAILED
LOG: http://maas-ci.internal:8080/job/maas/job/branch-tester/11234/console
COMMIT: d6a37d3691ade476bcc82e0addb6550523b399ff

review: Needs Fixing

[Alberto Donato (ack)]

+1

review: Approve

diff --git a/utilities/release-prepare b/utilities/release-prepare
index 8b5917b..13a1517 100755
--- a/utilities/release-prepare
+++ b/utilities/release-prepare
@@ -29,6 +29,10 @@ git_show_commit() {
     git show HEAD
 }
 
+version_changed() {
+    ! git diff --exit-code setup.cfg
+}
+
 deb_version() {
     local version
     version="$(echo "$1" | sed 's/a/~alpha/; tend; s/b/~beta/; tend; s/rc/~rc/; :end')"
@@ -91,6 +95,9 @@ if ! git_tree_clean; then
 fi
 
 replace_setup_version "$version"
+if ! version_changed; then
+    exit_error "The version is already set to $1"
+fi
 add_debian_changelog "$version"
 commit "$version"
 git_show_commit