Fix LOG.warn to LOG.warning

logging.warn is deprecated in Python 3.
https://docs.python.org/3/library/logging.html#logging.warning

Change-Id: I78774cd75ff78acd6a572e3e9f52ce52e2497594

fuelmenu/modules/bootstrapimg.py

@@ -359,8 +359,8 @@ class BootstrapImage(urwid.WidgetWrap):
             # repository since it is not created at that moment. Although we
             # still should provide an ability to use it, because in fact
             # it will be created at the end of deployment.
-            log.warn('Accessibility check is skipped for local repository: %s',
-                     release_url)
+            log.warning('Accessibility check is skipped for local '
+                        'repository: {}'.format(release_url))
             return True
 
         return self.check_url(release_url, proxies)

fuelmenu/modules/dnsandhostname.py

@@ -336,7 +336,7 @@ is accessible"}
                     if line.startswith("nameserver "):
                         nameservers.append(line.split(' ')[1])
         except EnvironmentError:
-            log.warn("Unable to open /etc/resolv.conf")
+            log.warning("Unable to open /etc/resolv.conf")
 
         # Always remove local IPs from nameserver list
         host_ips = network.list_host_ip_addresses()