btrfs-progs: convert tests: preserve test image permissions

If the test image is eg. on NFS it's not writable for root, so chmod
0777 fixes that but then we must not delete the file.

Signed-off-by: David Sterba <dsterba@suse.cz>

tests/convert-tests.sh

@@ -24,8 +24,10 @@ convert_test() {
 	nodesize=$2
 	shift 2
 	echo "creating ext image with: $*" >> $RESULTS
+	# IMAGE not removed as the file might have special permissions, eg.
+	# when test image is on NFS and would not be writable for root
+	run_check truncate -s 0 $IMAGE
 	# 256MB is the smallest acceptable btrfs image.
-	run_check rm -f $IMAGE
 	run_check truncate -s 256M $IMAGE
 	run_check $* -F $IMAGE