Bug#13699303 - THREAD POOL PLUGIN IGNORES TIMEOUT.

PROBLEM: 
mysql provides a feature where in a session which is 
idle for a period specified by the wait_timeout variable
(whose value is in seconds), the session is closed
This feature is not present when we use thread pool.
FIX:
This patch implements the interface functions which is 
required to implement the wait_timeout functionality
in the thread pool plugin.

sql/sql_class.cc

@@ -254,6 +254,18 @@ PSI_thread *thd_get_psi(THD *thd)
   return thd->scheduler.m_psi;
 }
 
+/**
+  Get net_wait_timeout for THD object
+
+  @param thd            THD object
+
+  @retval               net_wait_timeout value for thread on THD
+*/
+ulong thd_get_net_wait_timeout(THD* thd)
+{
+  return thd->variables.net_wait_timeout;
+}
+
 /**
   Set reference to Performance Schema object for THD object
 
@@ -422,6 +434,17 @@ void thd_set_net_read_write(THD *thd, uint val)
   thd->net.reading_or_writing= val;
 }
 
+/**
+  Get reading/writing on socket from THD object
+  @param thd                       THD object
+
+  @retval               net.reading_or_writing value for thread on THD.
+*/
+uint thd_get_net_read_write(THD *thd)
+{
+  return thd->net.reading_or_writing;
+}
+
 /**
   Set reference to mysys variable in THD object