Bind connection close callback APIs to python binding

Add code in the python binding to cope with the new APIs
virConnectRegisterCloseCallback and
virConnectUnregisterCloseCallback. Also demonstrate their
use in the python domain events demo

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

libvirt-override-virConnect.py

@@ -287,3 +287,26 @@
             retlist.append(virSecret(self, _obj=secret_ptr))
 
         return retlist
+
+    def _dispatchCloseCallback(self, reason, cbData):
+        """Dispatches events to python user close callback"""
+        cb = cbData["cb"]
+        opaque = cbData["opaque"]
+
+        cb(self, reason, opaque)
+        return 0
+
+
+    def unregisterCloseCallback(self):
+        """Removes a close event callback"""
+        ret = libvirtmod.virConnectUnregisterCloseCallback(self._o)
+        if ret == -1: raise libvirtError ('virConnectUnregisterCloseCallback() failed', conn=self)
+
+    def registerCloseCallback(self, cb, opaque):
+        """Adds a close event callback, providing a notification
+         when a connection fails / closes"""
+        cbData = { "cb": cb, "conn": self, "opaque": opaque }
+        ret = libvirtmod.virConnectRegisterCloseCallback(self._o, cbData)
+        if ret == -1:
+            raise libvirtError ('virConnectRegisterCloseCallback() failed', conn=self)
+        return ret