Generate glance-manage.conf

As specified in the blueprint, we are only going to set log_file in the
configuration file for now, and we read it last in glance.cmd.manage.
This allows glance-manage to use the appropriate log-file and still
retain the settings it needs in glance-api.conf and glance-registry.conf

DocImpact

Change-Id: I87595a29634e6ffda4e1581d42a92dfe6f84044b
Implements: blueprint create-glance-manage-conf
Closes-bug: #1391211
Merge "Generate glance-manage.conf"