[infra-tests] Correct bug in stability script (#5051)

Defer the transformation from string to List until after all items have
been appended.

See https://travis-ci.org/w3c/web-platform-tests/jobs/208254823 for a demonstration of the error this addresses.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/5051

Received on Monday, 6 March 2017 16:54:23 UTC