runner: don't resume sessions if SessionTicketsDisabled is true.

Change-Id: I1cf4a11d66871fff71a5fa93e39471ffb40d3132
Reviewed-on: https://boringssl-review.googlesource.com/1821
Reviewed-by: Adam Langley <agl@google.com>

ssl/test/runner/handshake_server.go

@@ -302,6 +302,10 @@ Curves:
 func (hs *serverHandshakeState) checkForResumption() bool {
 	c := hs.c
 
+	if c.config.SessionTicketsDisabled {
+		return false
+	}
+
 	var ok bool
 	if hs.sessionState, ok = c.decryptTicket(hs.clientHello.sessionTicket); !ok {
 		return false