Add results processing tool and stage to the interop workflow.

[chris-wood]

Ready to go!

This change adds a new utility program to process the output of each interop test case and upload it to a remote server for storage. This will let us render the interop results (a la https://interop.seemann.io/) by querying the contents of the server.

[cjpatton]

Not sure how to review this, as I'm missing the context for the change. Can you provide a bit of context?

[cjpatton]

Following the instructions in the README, the last command does this:

$ ./bin/runner --client=cloudflare-go --server=boringssl --testcase=dc
Error generating test inputs.

[chris-wood]

Not sure how to review this, as I'm missing the context for the change. Can you provide a bit of context?

Sure: this just dumps the test output into a bucket so that we can view the data elsewhere. (This is similar to the QUIC interop runner, which uploads all test output artifacts to another server, and that server then renders the results.)

[cjpatton]

Unable to test, so take this approval with a grain of salt. One comment about logging in Go.

[xvzcf]

Fine by me. At some point we might want to separate all the cert, DC, etc. artifact generation utilities into another library but we can deal with that when we get there.