Redirect error messages from libvirt to debug logger

- Add debug level to devops logger. Without this debug messages
  are skipped

Related-Bug: #1578280
Change-Id: I72dee9c2072da7d2658c1f159696c583184839b8

devops/__init__.py

@@ -29,6 +29,7 @@ LOGGER_SETTINGS = {
     'disable_existing_loggers': False,
     'loggers': {
         'devops': {
+            'level': 'DEBUG',
             'handlers': ['log_file', 'console_output'],
         },
     },

devops/driver/libvirt/libvirt_driver.py

@@ -50,6 +50,7 @@ class _LibvirtManager(object):
 
     def __init__(self):
         libvirt.virInitialize()
+        libvirt.registerErrorHandler(_LibvirtManager._error_handler, self)
         self.connections = {}
 
     def get_connection(self, connection_string):
@@ -64,6 +65,13 @@ class _LibvirtManager(object):
             conn = self.connections[connection_string]
         return conn
 
+    def _error_handler(self, error):
+        # this handler redirects libvirt messages to debug logger
+        if len(error) > 2 and error[2] is not None:
+            logger.debug(error[2])
+        else:
+            logger.debug(error)
+
 
 LibvirtManager = _LibvirtManager()