crypto/tls: fix test data generation

crypto/tls: fix test data generation

- Multiple GetCertificate tests shared the same name and were
  overwriting each other, each test now has a unique name.
- expectAlert was not implemented in the data updater, the single
  test that used it has been replaced with a ClientHello failure
  test.

Fixes #10470

Change-Id: I500738f6302ffa863d7ee45d85fa8773155e0614
Reviewed-on: https://go-review.googlesource.com/8959
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>