wsrep_init_thd_for_schema: initialize THD::thr_create_utime

63620ca identfied that thr_create_utime
wasn't initialized and therefore couldn't be used origin copying
point for the initialization of other variables.

By replacing with a micotime_interval, we missed that the
THD has just been created, and thr_create_utime should be set too.

This hasn't hit any MSAN errors so far but its possible to access
thr_create_utime in some codepath so lets initialize it.

Author: grooverdan

sql/wsrep_schema.cc

@@ -720,7 +720,8 @@ static void wsrep_init_thd_for_schema(THD *thd)
   thd->security_ctx->skip_grants();
   thd->system_thread= SYSTEM_THREAD_GENERIC;
   thd->real_id=pthread_self(); // Keep purify happy
-  thd->prior_thr_create_utime= thd->start_utime= microsecond_interval_timer();
+  thd->prior_thr_create_utime= thd->start_utime=
+    thd->thr_create_utime= microsecond_interval_timer();
   /* No Galera replication */
   thd->variables.wsrep_on= 0;
   /* No binlogging */