NSS only enables compatibility mode on the server if the client
requested it by way of the session ID. This is slightly off as a client
has no way not to request it when offering a TLS 1.2 session, but it is
in the spec.

So our tests are usable for other stacks, send a fake session ID in the
runner by default. The existing EmptySessionID-TLS13* test asserts that
BoringSSL behaves as we expect it to on empty session IDs too. The
intent is that NSS will disable that test but can otherwise leave the
rest enabled.

Change-Id: I370bf90aba1805c2f6970ceee0d29ecf199f437d
Reviewed-on: https://boringssl-review.googlesource.com/26504
Reviewed-by: Steven Valdez <svaldez@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>