1. Modify setup.cfg to make command openstack database log enable run
correctlly. class EnableDatabaseInstanceLog should be in database_instances,
not in database_limits. This is a HIGH priority error.
2. Originally, trove log-enable will return a log info when execute successfully.
This change makes OSC log_enable acts like the origin troveclient enable_log.
Change-Id: I68c5ef451c8e6c7fb189d6270bad002da7ffc9a6