adding an iopub timout flag

Author: kbarnhart

test_notebooks.py

@@ -20,6 +20,7 @@ def _notebook_run(path):
         args = ["jupyter", "nbconvert", "--to", "notebook", "--execute",
           "--ExecutePreprocessor.kernel_name=python",
           "--ExecutePreprocessor.timeout=None",
+          "ExecutePreprocessor.iopub_timeout=100",
           "--output", fout.name, path]
         subprocess.check_call(args)