Add tests for SSL_peek.

SSL_peek works fine for us, but OpenSSL 1.1.0 regressed this
(https://github.com/openssl/openssl/issues/1563), and we don't have
tests either. Fix this.

SSL_peek can handle all weird events that SSL_read can, so use runner
and tell bssl_shim to do a SSL_peek + SSL_peek + SSL_read instead of
SSL_read. Then add tests for all the events we may discover.

Change-Id: I9e8635e3ca19653a02a883f220ab1332d4412f98
Reviewed-on: https://boringssl-review.googlesource.com/11090
Reviewed-by: Adam Langley <agl@google.com>

ssl/test/test_config.cc

diff --git a/ssl/test/test_config.cc b/ssl/test/test_config.cc
index 1f01166..b7dc511 100644
--- a/ssl/test/test_config.cc
+++ b/ssl/test/test_config.cc
@@ -104,6 +104,7 @@
     &TestConfig::use_old_client_cert_callback },
   { "-use-null-client-ca-list", &TestConfig::use_null_client_ca_list },
   { "-send-alert", &TestConfig::send_alert },
+  { "-peek-then-read", &TestConfig::peek_then_read },
 };
 
 const Flag<std::string> kStringFlags[] = {