Stop watchdog on power off

Stop watchdog if any on a power off request so that it does not
expire if the system is powered off in the middle of a power on.
Clear any existing watchdog timers before honoring a start
watchdog request so that there is only one timer at a time.
diff --git a/bin/chassis_control.py b/bin/chassis_control.py
index 2ed954e..e8c82d5 100755
--- a/bin/chassis_control.py
+++ b/bin/chassis_control.py
@@ -118,6 +118,8 @@
 		in_signature='', out_signature='')
 	def powerOff(self):
 		print "Turn off power"
+		intfwatchdog = self.getInterface('watchdog')
+		intfwatchdog.stop()
 		intf = self.getInterface('power_control')
 		intf.setPowerState(POWER_OFF)
 		return None