trillian/integration: refactor integration test
trillian/integration: refactor integration test

Use a testInfo structure to hold per-test info and make more
complicated functions into methods on that structure.

daviddrysdale/certificate-transparency-go,google/certificate-transparency-go,RJPercival/certificate-transparency-go,google/certificate-transparency-go,google/certificate-transparency-go,daviddrysdale/certificate-transparency-go,RJPercival/certificate-transparency-go,daviddrysdale/certificate-transparency-go,RJPercival/certificate-transparency-go