[infra-tests] DEBUG Capture output from timeout (#5708)

This branch is being used as part of an investigation on intermittent
failures in the continuous integration environment. It is not intended
to be merged to `master`.

Update the build script to output additional debugging information.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/5708

Received on Wednesday, 26 April 2017 18:46:40 UTC