Correct use of ConfigFilesNotFoundError

ConfigFilesNotFoundError.__init__() takes "config_files", not
"path". And pass the config value itself rather than the result
of find_file(), which is always None.

Change-Id: Ia5285d252d5636892c4fbeb9191a6c7ed4923b78
Closes-Bug: 1236176
(cherry picked from commit 84b02ca1d54fd058c68345068832e84d2f80b9a5)
Merge "Correct use of ConfigFilesNotFoundError" into milestone-proposed