Skip tests that use whiteouts under Docker/aufs

ostree's naming convention for whiteouts is similar to what is
done in aufs, which means we can't compose the trees to test this
feature under Docker with the aufs storage driver, as used on
travis-ci.

Signed-off-by: Simon McVittie <smcv@debian.org>

Closes: #437
Approved by: cgwalters

tests/basic-test.sh

@@ -452,8 +452,7 @@ echo "ok test error pre commit/bootid"
 # Whiteouts
 cd ${test_tmpdir}
 mkdir -p overlay/baz/
-touch overlay/baz/.wh.cow
-touch overlay/.wh.deeper
+if touch overlay/baz/.wh.cow && touch overlay/.wh.deeper; then
     touch overlay/anewfile
     mkdir overlay/anewdir/
     touch overlay/anewdir/blah
@@ -484,6 +483,10 @@ assert_not_has_dir overlay-co/deeper
     assert_has_file overlay-co/anewdir/blah
     assert_has_file overlay-co/anewfile
     echo "ok whiteouts disabled"
+else
+    echo "ok # SKIP whiteouts do not work, are you using aufs?"
+    echo "ok # SKIP whiteouts do not work, are you using aufs?"
+fi
 
 cd ${test_tmpdir}
 rm -rf test2-checkout