Move snapd to edge for the TPM FDE snaps

We need edge on the live session too so that subiquity knows about
latest and greatest on TPM FDE support. We will revert that once snapd
is released to the stable channel.

live-build/functions

@@ -565,8 +565,13 @@ _snap_post_process() {
         core[0-9]*)
             # If the 'core' snap is not present, assume we are coreXX-only and
             # install the snapd snap.
+            channel=stable
+            # FIXME: TPM-FDE spike, to be removed after the spike is over.
+            if [ $PROJECT = "ubuntu" ]; then
+                channel=edge
+            fi
             if [ ! -f ${snaps_dir}/core_[0-9]*.snap ]; then
-                _snap_preseed $CHROOT_ROOT snapd stable
+                _snap_preseed $CHROOT_ROOT snapd "$channel"
             fi
             ;;
         core)