Workaround broken package update

After spending days debugging, it was determined that upgrading
cloud-init results in a failure to add/update OSLogin users
(and ssh keys) upon reboot (after resetting the system).
The exact cause is unknown and further/deeper debugging
isn't worth the effort.  Workaround the problem by
blocking the update for now

base_images/ubuntu_base-setup.sh

@@ -28,6 +28,14 @@ PKGS=( \
 )
 
 $SUDO apt-get -qq -y update
+
+# At the time of this commit, upgrading past the stock
+# cloud-init (21.3-1-g6803368d-0ubuntu1~21.04.3) causes
+# failure of login w/ new ssh key after reset + reboot.
+if ! ((CONTAINER)); then
+    $SUDO apt-mark hold cloud-init
+fi
+
 $SUDO apt-get -qq -y upgrade
 $SUDO apt-get -qq -y install "${PKGS[@]}"