skimage: if --readPath points at an empty dir, create an empty expectations file

tools/tests/skimage/output-expected/nonexistent-dir/expectations.json

Index: tools/tests/skimage/output-expected/nonexistent-dir/expectations.json
===================================================================
--- tools/tests/skimage/output-expected/nonexistent-dir/expectations.json	(revision 0)
+++ tools/tests/skimage/output-expected/nonexistent-dir/expectations.json	(revision 0)
@@ -0,0 +1,9 @@
+{
+   "actual-results" : {

[epoger, 2013/06/17 19:34:47]

Currently, this case (--readPath pointing at a directory that does not exist)
yields identical results to being called for an empty directory.

We may want to change that-- it seems to me that readPath pointing at a
directory that doesn't exist is more of an error case.

+      "failed" : null,
+      "failure-ignored" : null,
+      "no-comparison" : null,
+      "succeeded" : null
+   },
+   "expected-results" : null
+}