Moved the housekeeper heartbeat to a separate header for ease of integration.

This keeps the behavior the same but allows the heartbeat to be used as a crude timer
without including everything the housekeeper.h header includes.

Moved the protocol level updates on the DCBs last_read value into dcb_read.
This keeps the implementation nice and compact.

server/modules/protocol/maxscaled.c

@@ -144,9 +144,7 @@ char		*password;
 
 	if ((n = dcb_read(dcb, &head)) != -1)
 	{
-	    
-	dcb->last_read = hkheartbeat;
-	
+
 		if (head)
 		{
 			unsigned char *ptr = GWBUF_DATA(head);