tar2fs: chgrp and failsafe kpartx

The current state made vm images belong to root group,
no reason to not change those to the primary group of
the user building an image.

kpartx -d -s could fail in some circumstances,
make a safety cleanup call more verbose.

bin/tar2fs

@@ -138,7 +138,10 @@ exit_handler() {
 		umount ${BOOTFS:+"$BOOTFS"} "$ROOTFS"{/dev,/proc,/sys,}
 
 		if [ -n "$LOOPDEV" ]; then
-			kpartx -d -s "$LOOPDEV"
+			kpartx -d -s "$LOOPDEV" || {
+				sleep 10
+				kpartx -d -s -v "$LOOPDEV"
+			}
 			losetup --detach "$LOOPDEV"
 		fi
 		rm -r -- "$ROOTFS"
@@ -272,5 +275,5 @@ image=/boot/vmlinuz
 fi
 
 if [ -n "$SUDO_USER" ]; then
-	chown "$SUDO_USER" "$IMG" "$ROOTFS" "$WORKDIR"
+	chown "$SUDO_USER:$(id -g "$SUDO_USER")" "$IMG" "$ROOTFS" "$WORKDIR" ||:
 fi