Improved a test error message and logged an issue: DVPL-6701

In short tests.test_examples.ExamplesTestCase#test_index consistently
fails when asked to run "index.py clean sdk-tests"

Author: David Noble

tests/data/custom_search/usercount.out

@@ -0,0 +1,10 @@
+Traceback (most recent call last):
+  File "custom_search/bin/usercount.py", line 182, in <module>
+    main(sys.argv)
+  File "custom_search/bin/usercount.py", line 149, in main
+    buf, settings = read_input(stdin_wrapper, has_header = True)
+  File "custom_search/bin/usercount.py", line 109, in read_input
+    line = buf.readline()
+  File "custom_search/bin/usercount.py", line 58, in readline
+    raise StopIteration
+StopIteration