Add machinery for testing TLS 1.3 cipher change synchronization.
This will be used for writing the equivalent test in TLS 1.3 to the
recent DTLS change and similar.
Change-Id: I280c3ca8f1d8e0981b6e7a499acb7eceebe43a0c
Reviewed-on: https://boringssl-review.googlesource.com/8792
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>