Add tests for failing cert_cb.

We missed that the TLS 1.3 code was inconsistent with the TLS 1.2 code.
Only on the server did we push an error code. But consistency between
client and server is probably worthwhile so, fix the 1.2 code to match
for now.

Change-Id: I17952c72048697dc66eacf0f144a66ced9cb3be8
Reviewed-on: https://boringssl-review.googlesource.com/12260
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>
diff --git a/ssl/test/test_config.cc b/ssl/test/test_config.cc
index 470f034..4f40df9 100644
--- a/ssl/test/test_config.cc
+++ b/ssl/test/test_config.cc
@@ -75,6 +75,7 @@
   { "-install-ddos-callback", &TestConfig::install_ddos_callback },
   { "-fail-ddos-callback", &TestConfig::fail_ddos_callback },
   { "-fail-second-ddos-callback", &TestConfig::fail_second_ddos_callback },
+  { "-fail-cert-callback", &TestConfig::fail_cert_callback },
   { "-handshake-never-done", &TestConfig::handshake_never_done },
   { "-use-export-context", &TestConfig::use_export_context },
   { "-tls-unique", &TestConfig::tls_unique },