Copy common.csv and diff.csv into DIST_DIR

Bug: 138639389
Test: DIST_DIR=... compare_image_and_print.sh ~~ and then check if there
are files in DIST_DIR

Change-Id: Ia3efde82429abb740b9deb93b4c87c0b45a0217a
diff --git a/vndk/tools/image-diff-tool/compare_images_and_print.sh b/vndk/tools/image-diff-tool/compare_images_and_print.sh
index fc8b67b..9dd958d 100755
--- a/vndk/tools/image-diff-tool/compare_images_and_print.sh
+++ b/vndk/tools/image-diff-tool/compare_images_and_print.sh
@@ -8,3 +8,7 @@
 echo
 echo " - Different parts"
 cat diff.csv
+
+if [ -v DIST_DIR ]; then
+  cp common.csv diff.csv $DIST_DIR
+fi