Set libvirt environment variables to deactivate logging

cloudcontrol/node/node.py

+import os
 import time
 import signal
 import logging
@@ -152,6 +153,10 @@ class RPCStartHandler(Thread):
             if self.loop.role is not None:
                 self.loop.close_plugins()
             logger.debug('Role hypervisor affected')
+            # set libvirt environement variables
+            os.environ['LIBVIRT_DEBUG'] = '4'
+            # os.environ['LIBVIRT_LOG_FILTERS'] = ''
+            os.environ['LIBVIRT_LOG_OUTPUT'] = '4:stderr'
             # we don't import those modules at the top because some dependancies
             # may not be installed
             from cloudcontrol.node.hypervisor import Handler as HypervisorHandler