Handle seeded lxd snap with channel name for ubuntu-cpc:minimized

The seed now specifies the lxd snap in focal as
'lxd=4.0/stable/ubuntu-20.04' which doesn't match the expectations of
the code with looks for lxd as the only snap in the seed for minimized
images.  This patch updates the pattern to accept 'lxd' or 'lxd=*'.

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (2.679) groovy; urgency=medium
+
+  *  Handle seeded lxd snap with channel name for ubuntu-cpc:minimized
+     (LP: #1889470)
+
+ -- Robert C Jennings <robert.jennings@canonical.com>  Wed, 29 Jul 2020 14:55:57 -0500
+
 livecd-rootfs (2.678) groovy; urgency=medium
 
   [ David Krauser ]

live-build/auto/config

@@ -872,7 +872,7 @@ if [ "$PROJECT:${SUBPROJECT:-}" = ubuntu-cpc:minimized ]; then
 	# build if we see such a snap.
 	for snap in `cat config/seeded-snaps`; do
 		case $snap in
-			lxd)
+			lxd | lxd=*)
 				;;
 			*)
 				echo "Unexpected seeded snap for ubuntu-cpc:minimized build: $snap"