Add test for docker aufs whiteout

tests/21-build_docker.sh

@@ -60,6 +60,12 @@ stest 1 sudo singularity build -F "$CONTAINER" docker://something_that_doesnt_ex
 stest 1 singularity exec "$CONTAINER" true
 stest 1 singularity exec "$CONTAINER" false
 
+# AUFS sanity tests
+stest 0 sudo singularity build -F "$CONTAINER" docker://dctrud/docker-aufs-sanity
+stest 0 singularity exec "$CONTAINER" ls /test/whiteout-dir/file2 /test/whiteout-file/file2 /test/normal-dir/file2
+stest 1 singularity exec "$CONTAINER" ls /test/whiteout-dir/file1 /test/whiteout-file/file1
+stest 1 singularity exec "$CONTAINER" ls /test/*/.wh*
+
 if singularity_which docker >/dev/null 2>&1; then
 # make sure local test does not exist, ignore errors
 sudo docker kill registry >/dev/null 2>&1