Cut over to generating new HMAC-based XSRF tokens

This is the second step of migrating to our new XSRF token format.  The
first step ([] made validate() start accepting new tokens
(basically, dual-read).  This step cuts over our "writing" to write the
new token format.  The third and final step will drop support for
validating the old token format (back to single-read).  We'll do that
in a subsequent push so that we don't invalidate all the current XSRF
tokens that people might have in their browsers.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=149790648

java/google/registry/loadtest/LoadTestAction.java

@@ -183,7 +183,7 @@ public class LoadTestAction implements Runnable {
     xmlHostCreateTmpl = loadXml("host_create");
     xmlHostCreateFail = xmlHostCreateTmpl.replace("%host%", EXISTING_HOST);
     xmlHostInfo = loadXml("host_info").replace("%host%", EXISTING_HOST);
-    xsrfToken = xsrfTokenManager.generateLegacyToken("admin", "");
+    xsrfToken = xsrfTokenManager.generateToken("");
   }
 
   @Override