Added some assertions to testHandshake, but avoided checking the error
of one of the Close() because the one that would lose the race would
write the closeNotify to a connection closed on the other side which is
broken on js/wasm (#28650). Moved that Close() after the chan sync to
ensure it happens second.

Accepting a ticket with client certificates when NoClientCert is
configured is probably not a problem, and we could hide them to avoid
confusing the application, but the current behavior is to skip the
ticket, and I'd rather keep behavior changes to a minimum.

Updates #9671

Change-Id: I93b56e44ddfe3d48c2bef52c83285ba2f46f297a
Reviewed-on: https://go-review.googlesource.com/c/147445Reviewed-by: Adam Langley <agl@golang.org>