Capture github test artifacts for failed builds

I submitted a pull request (https://travis-ci.org/apache/thrift/jobs/68196878) which had a lot of failures. I want to see the output from "make cross" tests that failed because it does not fail for me locally. I have no way of knowing how these tests failed in the build environment.

Resolved: click on after_failure in travis at the end to get the client and server logs.