Merge "Add option to skip update packages"

diskimage_builder/elements/base/README.rst

@@ -20,6 +20,14 @@ customize cloud-init's management of `/etc/hosts`:
    preserve diskimage-builder's current default behavior in the
    future, set the variable to "localhost" explicitly.)
 
+The 'DIB_AVOID_PACKAGES_UPDATE' environment variable can be used to
+avoid updating all packages, useful when wanting to avoid release
+update.
+
+ * 'DIB_AVOID_PACKAGES_UPDATE' default is '0', all packages will be updated.
+
+ * set 'DIB_AVOID_PACKAGES_UPDATE' to '1' to avoid updating all packages.
+
 Notes:
 
  * If you are getting warnings during the build about your locale

diskimage_builder/elements/base/environment.d/10-base-defaults

@@ -0,0 +1 @@
+export DIB_AVOID_PACKAGES_UPDATE=${DIB_AVOID_PACKAGES_UPDATE:-0}

diskimage_builder/elements/base/install.d/00-up-to-date

@@ -8,4 +8,6 @@ fi
 set -eu
 set -o pipefail
 
-install-packages -u
+if [ ${DIB_AVOID_PACKAGES_UPDATE} -eq 0 ]; then
+    install-packages -u
+fi