MW-292 Reset timestamp after transaction replay

Transaction replay causes the THD to re-apply the replication
events from execution, using the same path appliers do. While
applying the log events, the THD's timestamp is set to the
timestamp of the event.
Setting the timestamp explicitly causes function NOW() to
always the timestamp that was set. To avoid this behavior we
reset the timestamp after replaying is done.

sql/sql_class.h

@@ -68,6 +68,7 @@ struct wsrep_thd_shadow {
   ulong                tx_isolation;
   char                 *db;
   size_t               db_length;
+  my_hrtime_t          user_time;
 };
 #endif
 class Reprepare_observer;

sql/wsrep_thd.cc

@@ -160,6 +160,7 @@ static void wsrep_prepare_bf_thd(THD *thd, struct wsrep_thd_shadow* shadow)
 
   shadow->db            = thd->db;
   shadow->db_length     = thd->db_length;
+  shadow->user_time     = thd->user_time;
   thd->reset_db(NULL, 0);
 }
 
@@ -170,6 +171,7 @@ static void wsrep_return_from_bf_mode(THD *thd, struct wsrep_thd_shadow* shadow)
   thd->wsrep_exec_mode        = shadow->wsrep_exec_mode;
   thd->net.vio                = shadow->vio;
   thd->variables.tx_isolation = shadow->tx_isolation;
+  thd->user_time              = shadow->user_time;
   thd->reset_db(shadow->db, shadow->db_length);
 
   delete thd->system_thread_info.rpl_sql_info;