Run "snap debug validate-seed" to do basic validation of the generated seed.yaml

(cherry picked from commit b208ded59e)

Signed-off-by: Iain Lane <iain.lane@canonical.com>

debian/control

@@ -33,7 +33,7 @@ Depends: ${misc:Depends},
          python3-software-properties,
          qemu-utils,
          rsync,
-         snapd,
+         snapd (>= 2.39),
          squashfs-tools (>= 1:3.3-1),
          sudo,
          u-boot-tools [armhf arm64],

live-build/functions

@@ -579,6 +579,15 @@ snap_preseed() {
             touch "$CHROOT_ROOT/var/lib/snapd/seed/.snapd-explicit-install-stamp"
             ;;
     esac
+
+
+    # Do basic validation of generated snapd seed.yaml, doing it here
+    # means we catch all the places(tm) that snaps are added but the
+    # downside is that each time a snap is added the seed must be valid,
+    # i.e. snaps with bases need to add bases first etc.
+    if [ -e chroot/var/lib/snapd/seed/seed.yaml ]; then
+        snap debug validate-seed "$CHROOT_ROOT/var/lib/snapd/seed/seed.yaml"
+    fi
 }
 
 is_live_layer () {