git_auto_update: Added and used error function

roles/git_auto_update/templates/update.sh

@@ -9,6 +9,10 @@ readonly DEST_GROUP={{ group | quote }};
 readonly PREFIX={{ tag_prefix | quote }};
 readonly GPG_FINGERPRINT={{ gpg_fingerprint | quote }};
 
+function error() {
+  echo "$@" >&2;
+}
+
 cd "$DEST";
 
 if [ ! -d .git ]; then
@@ -26,10 +30,10 @@ if [ -z "$GPG_FINGERPRINT" ] || (git verify-tag --raw "$TAG" 2>&1 | grep --fixed
   git checkout --quiet --recurse-submodules "$TAG";
   chown --recursive "$DEST_USER:$DEST_GROUP" .;
   if ! sh -c {{ reload_command | default('true') | quote }}; then
-    echo "Reload command failed" >&2;
+    error "Reload command failed";
     exit 2;
   fi
 else
-  echo "Invalid or missing signature for $TAG" >&2;
+  error "Invalid or missing signature for $TAG";
   exit 1;
 fi