update-{all,packages} build profile action: empty packages dir

... before copying the new contents to the image. This caters to the
typical use case of updating an existing Haiku, making manual
intervention to get the new packages activated unnecessary. The downside
is that manually added packages will be removed as well.

build/jam/ImageRules

@@ -840,6 +840,9 @@ rule AddPackagesAndRepositoryVariablesToContainerScript script : container
 	AddVariableToScript $(script) : resolvePackageDependencies
 		: $(resolvePackageDependencies) ;
 
+	AddVariableToScript $(script) : updateAllPackages
+		: $(HAIKU_UPDATE_ALL_PACKAGES) ;
+
 	# Add variable "systemPackages"  with the packages copied/updated.
 	local allPackages = [ on $(container) return $(HAIKU_PACKAGES_IN_IMAGE) ] ;
 	if $(updateOnly) && ! [ IncludeAllTargetsInContainer $(container) ] {

build/scripts/build_haiku_image

@@ -16,6 +16,7 @@ set -o errexit
 # imageSize
 # imageLabel
 # resolvePackageDependencies
+# updateAllPackages
 # updateOnly
 # dontClearImage
 # isVMwareImage
@@ -269,6 +270,15 @@ if [ $isImage ]; then
 	$cd .
 fi
 
+
+# Clean out the old packages directory, if updating all packages.
+if [ -n "$updateAllPackages" ]; then
+	echo "Removing old packages ..."
+	$rm -rf "${tPrefix}system/packages"
+	$mkdir -p "${tPrefix}system/packages"
+fi
+
+
 echo "Populating image ..."
 while [ $# -gt 0 ]; do
 	. $1