guestfish: move set-label after mkfs

Fixes:

libguestfs: error: set_label: don't know how to set the label for '' filesystems

hooks/merged-usr/essential00.sh

@@ -8,8 +8,20 @@ fi
 
 TARGET="$1"
 
-APT_CONFIG=$MMDEBSTRAP_APT_CONFIG apt-get --yes install -oDPkg::Chroot-Directory="$TARGET" usr-is-merged
-
-chroot "$TARGET" dpkg-query --showformat '${db:Status-Status}\n' --show usr-is-merged | grep -q '^installed$'
-chroot "$TARGET" dpkg-query --showformat '${Source}\n' --show usr-is-merged | grep -q '^usrmerge$'
-dpkg --compare-versions "1" "lt" "$(chroot "$TARGET" dpkg-query --showformat '${Version}\n' --show usr-is-merged)"
+if [ "${MMDEBSTRAP_MODE:-}" = "chrootless" ]; then
+	APT_CONFIG=$MMDEBSTRAP_APT_CONFIG apt-get --yes install \
+		-oDPkg::Options::=--force-not-root \
+		-oDPkg::Options::=--force-script-chrootless \
+		-oDPkg::Options::=--root="$TARGET" \
+		-oDPkg::Options::=--log="$TARGET/var/log/dpkg.log" \
+		usr-is-merged
+	export DPKG_ROOT="$TARGET"
+	dpkg-query --showformat '${db:Status-Status}\n' --show usr-is-merged | grep -q '^installed$'
+	dpkg-query --showformat '${Source}\n' --show usr-is-merged | grep -q '^usrmerge$'
+	dpkg --compare-versions "1" "lt" "$(dpkg-query --showformat '${Version}\n' --show usr-is-merged)"
+else
+	APT_CONFIG=$MMDEBSTRAP_APT_CONFIG apt-get --yes install -oDPkg::Chroot-Directory="$TARGET" usr-is-merged
+	chroot "$TARGET" dpkg-query --showformat '${db:Status-Status}\n' --show usr-is-merged | grep -q '^installed$'
+	chroot "$TARGET" dpkg-query --showformat '${Source}\n' --show usr-is-merged | grep -q '^usrmerge$'
+	dpkg --compare-versions "1" "lt" "$(chroot "$TARGET" dpkg-query --showformat '${Version}\n' --show usr-is-merged)"
+fi

mmdebstrap

@@ -1858,18 +1858,14 @@ sub run_setup() {
         close $fh;
     }
 
-    # we create /var/lib/dpkg/arch inside the chroot either if there is more
-    # than the native architecture in the chroot or if chrootless mode is
-    # used to create a chroot of a different architecture than the native
-    # architecture outside the chroot.
+    # In theory, /var/lib/dpkg/arch is only useful if there are foreign
+    # architectures configured or if the architecture of a chrootless chroot
+    # is different from the native architecture outside the chroot.
+    # We nevertheless always add /var/lib/dpkg/arch to make a chroot built the
+    # normal way bit-by-bit identical to a foreign arch chroot built in
+    # chrootless mode.
     chomp(my $hostarch = `dpkg --print-architecture`);
-    if (
-        (!-e "$options->{root}/var/lib/dpkg/arch")
-        and (
-            scalar @{ $options->{foreignarchs} } > 0
-            or (    $options->{mode} eq 'chrootless'
-                and $hostarch ne $options->{nativearch}))
-    ) {
+    if ((!-e "$options->{root}/var/lib/dpkg/arch")) {
         open my $fh, '>', "$options->{root}/var/lib/dpkg/arch"
           or error "cannot open /var/lib/dpkg/arch: $!";
         print $fh "$options->{nativearch}\n";
@@ -4001,6 +3997,7 @@ sub get_sourceslist_by_suite {
             variants() { :; };
             keyring() { :; };
             doing_variant() { false; };
+            info() { fmt="$2"; shift; shift; printf "I: $fmt\n" "$@" >&2; };
             . /usr/share/debootstrap/scripts/gutsy;';
             open my $fh, '-|', 'env', "ARCH=$arch", "SUITE=$suite",
               'sh', '-c', $script // last;
@@ -6949,8 +6946,9 @@ Create a bootable USB Stick that boots into a full Debian desktop:
     $ guestfish -N debian-unstable.img=disk:8G -- \
         part-disk /dev/sda mbr : \
         part-set-bootable /dev/sda 1 true : \
+        mkfs ext4 /dev/sda1 : \
         set-label /dev/sda1 rootfs : \
-        mkfs ext4 /dev/sda1 : mount /dev/sda1 / : \
+        mount /dev/sda1 / : \
         tar-in debian-unstable.tar / xattrs:true : \
         upload /usr/lib/EXTLINUX/mbr.bin /boot/mbr.bin : \
         copy-file-to-device /boot/mbr.bin /dev/sda size:440 : \
@@ -6964,8 +6962,9 @@ On architectures without extlinux you can also boot using grub2:
     $ guestfish -N debian-unstable.img=disk:2G -- \
         part-disk /dev/sda mbr : \
         part-set-bootable /dev/sda 1 true : \
+        mkfs ext4 /dev/sda1 : \
         set-label /dev/sda1 rootfs : \
-        mkfs ext4 /dev/sda1 : mount /dev/sda1 / : \
+        mount /dev/sda1 / : \
         tar-in fs.tar / xattrs:true : \
         command "grub-install /dev/sda" : \
         command update-grub : \