Avoid FutureWarning from Numpy

tests/test_numpyclient.py

@@ -176,9 +176,9 @@ class TestNumpyClient(object):
         in_("error parsing input data", str(e.exception))
 
         # Make sure the /newton/prep copies are identical
-        a = np.vstack(client.stream_extract_numpy("/newton/prep"))
-        b = np.vstack(client.stream_extract_numpy("/test/2"))
-        c = np.vstack(client.stream_extract_numpy("/test/3"))
+        a = np.vstack(list(client.stream_extract_numpy("/newton/prep")))
+        b = np.vstack(list(client.stream_extract_numpy("/test/2")))
+        c = np.vstack(list(client.stream_extract_numpy("/test/3")))
         assert(np.array_equal(a,b))
         assert(np.array_equal(a,c))