Change the name of logfile to be consistenet

Name of the logfile specified in the conf file was discovery.log, changing it
to contrail-discovery.log

Change-Id: I1db7c2661472ef8ea1fff4ef45cae068711bc585
Closes-Bug: 1524678

contrail_provisioning/config/common.py

@@ -245,7 +245,7 @@ def fixup_discovery_config_file(self):
                          '__contrail_listen_ip_addr__': '0.0.0.0',
                          '__contrail_listen_port__': '5998',
                          '__contrail_log_local__': 'True',
-                         '__contrail_log_file__': '/var/log/contrail/discovery.log',
+                         '__contrail_log_file__': '/var/log/contrail/contrail-discovery.log',
                          '__contrail_healthcheck_interval__': 5,
                          '__contrail_cassandra_server_list__' : ' '.join('%s:%s' % cassandra_server for cassandra_server in self.cassandra_server_list),
                         }