Previously, if a submodule skipped test classes in an adjacent submodule (same
parent module), only the running submodule was imported and an error was thrown
because getattr would not find the submodule of the to-be-skipped class. Updated
cached_import in django/utils/module_loading.py to include a check for the skipped
submodule, and import it if it is not there.
Thanks to Tim Graham for reporting this bug