pre-upload_unittest: handle newer test api

The chromite main func updated its api to need the caller pass in its
module name explicitly.

BUG=chromium:219660
TEST=`./pre-upload_unittest.py` still passes

Change-Id: I2abf980896b07b88a941ba427a3d4e7151f364e2
Reviewed-on: https://chromium-review.googlesource.com/271644
Reviewed-by: Dan Erat <derat@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/pre-upload_unittest.py b/pre-upload_unittest.py
index c073a01..57642fd 100755
--- a/pre-upload_unittest.py
+++ b/pre-upload_unittest.py
@@ -1042,4 +1042,4 @@
 
 
 if __name__ == '__main__':
-  cros_test_lib.main()
+  cros_test_lib.main(module=__name__)