test_lists.py: Skip generic test list if main test list exists

If there is a main.py file or a test list object 'main' has been
loaded, generic test list should be skipped.
Then if main test list has bug, goofy will try to load it and show the
error instead of falling back to generic test list.

BUG=None
TEST=run goofy with main.py exists and with bug.

Change-Id: I6540ad7201337a649eeb8417db04a39a55bffb73
Reviewed-on: https://chromium-review.googlesource.com/186879
Reviewed-by: Bowgo Tsai <bowgotsai@chromium.org>
Commit-Queue: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
1 file changed