Handle error that occurs when the log directory isn't present

[chrisranderson]

Here is the error:

E0906 20:52:03.265715 Thread-324 _internal.py:87] Error on request:
Traceback (most recent call last):
  File "/home/chris/.cache/bazel/_bazel_chris/8d1807db289ed3ede825379035a2931f/external/org_pocoo_werkzeug/werkzeug/serving.py", line 193, in run_wsgi
    execute(self.server.app)
  File "/home/chris/.cache/bazel/_bazel_chris/8d1807db289ed3ede825379035a2931f/external/org_pocoo_werkzeug/werkzeug/serving.py", line 181, in execute
    application_iter = app(environ, start_response)
  File "/home/chris/.cache/bazel/_bazel_chris/8d1807db289ed3ede825379035a2931f/external/org_tensorflow_tensorboard/tensorboard/backend/application.py", line 239, in __call__
    return self.data_applications[clean_path](environ, start_response)
  File "/home/chris/.cache/bazel/_bazel_chris/8d1807db289ed3ede825379035a2931f/external/org_pocoo_werkzeug/werkzeug/wrappers.py", line 291, in application
    return f(*args[:-2] + (request,))(*args[-2:])
  File "/home/chris/school-projects/beholder/beholder/server_side/beholder_plugin.py", line 114, in _serve_change_config
    write_pickle(config, '{}/{}'.format(self.PLUGIN_LOGDIR, CONFIG_FILENAME))
  File "/home/chris/school-projects/beholder/beholder/file_system_tools.py", line 33, in write_pickle
    pickle.dump(obj, new_file)
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/lib/io/file_io.py", line 102, in write
    self._prewrite_check()
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/lib/io/file_io.py", line 88, in _prewrite_check
    compat.as_bytes(self.__name), compat.as_bytes(self.__mode), status)
  File "/usr/lib/python3.5/contextlib.py", line 66, in __exit__
    next(self.gen)
  File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/framework/errors_impl.py", line 466, in raise_exception_on_not_ok_status
    c_api.TF_GetCode(status))
tensorflow.python.framework.errors_impl.NotFoundError: /tmp/beholder-demo/plugins/beholder/config.pkl; No such file or directory