MDEV-6975 Implement TLS protocol

followup:
* explicitly disable SSLv2 and SSLv3, keep other protocols enabled
* fix a compiler warning
* rename the test and combinations to avoid confusion

vio/viossl.c:
  fix a compiler warning

mysql-test/t/openssl_6975.combinations

@@ -1,6 +1,6 @@
 [tlsv12]
 loose-ssl-cipher=TLSv1.2
 
-[sslv3]
+[tlsv10]
 loose-ssl-cipher=SSLv3
 

vio/viossl.c

@@ -144,7 +144,7 @@ int vio_ssl_close(Vio *vio)
       break;
     default: /* Shutdown failed */
       DBUG_PRINT("vio_error", ("SSL_shutdown() failed, error: %d",
-                               SSL_get_error(ssl, r)));
+                               (int)SSL_get_error(ssl, r)));
       break;
     }
   }

vio/viosslfactories.c

@@ -200,6 +200,8 @@ new_VioSSLFd(const char *key_file, const char *cert_file,
     DBUG_RETURN(0);
   }
 
+  SSL_CTX_set_options(ssl_fd->ssl_context, SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3);
+
   /*
     Set the ciphers that can be used
     NOTE: SSL_CTX_set_cipher_list will return 0 if