Supports cold reset in bmc

The spec [1] is trying to support nmi, so that
we should also enhance bmc to support it.

[1] I3dc6561ea7cecf8b8d998717fefa9cf8001d0f4c

Change-Id: Ib7465ace5b370b31dab5334a34f7216170e1ff2b

pyghmi/ipmi/bmc.py

@@ -72,6 +72,9 @@ class Bmc(serversession.IpmiServer):
                 rc = self.power_cycle()
             elif directive == 3:
                 rc = self.power_reset()
+            elif directive == 4:
+                # i.e. a NMI reset
+                rc = self.cold_reset()
             elif directive == 5:
                 rc = self.power_shutdown()
             if rc is None: