Both sides of the merge tested the same behavior. Keep one test of
each: ClientCertStillRequired* for a server keeping client certificates
required, which covers a cleared callback too, VerifierStaysWithItsClient
for per-client verifiers across threads, and the Keep* redirect tests,
which share one helper. KeepSessionVerifier now also checks the error,
as the dropped SessionVerifier did.
yhirose
2594f17983
