[infra-tests] Ignore .rej files in web-platform-tests, (#5082)

This ensures that they are not added to the manifest.

MozReview-Commit-ID: 5blMXYYNV8U

Upstreamed from https://bugzilla.mozilla.org/show_bug.cgi?id=1342062

View on GitHub: https://github.com/w3c/web-platform-tests/pull/5082

Received on Wednesday, 8 March 2017 14:02:53 UTC