Add oslo_log command options to magnum-db-manage

As we all know, 'command magnum-api' and 'magnum-conductor' have
many options such as 'log-file' and 'use-syslog'. But as for
magnum-db-magnum, these are not available.
Add oslo_log command options will help.

Change-Id: If61efbde56e1d7dd0ed88d76fa42dd00501cc938

magnum/cmd/db_manage.py

@@ -14,6 +14,7 @@
 """Starter script for magnum-db-manage."""
 
 from oslo_config import cfg
+from oslo_log import log as logging
 
 from magnum.db import migration
 
@@ -63,6 +64,7 @@ command_opt = cfg.SubCommandOpt('command',
 
 
 def main():
+    logging.register_options(CONF)
     CONF.register_cli_opt(command_opt)
 
     CONF(project='magnum')