Create and use configuration file for glance-manage

Currently glance-manage uses glance-registry and glance-api's configuration files for different values and ends up attempting to log to glance-api's log file. This can lead to permissions errors when trying to use glance-manage as a separate user on the system. It would be better if glance-manage had its own configuration file so that it could be configured without also affecting glance-registry and glance-api.