To prepare for object-expirer's general task queue feature [1],
this patch enables to configure object-expirer in object-server.conf.
Object-expirer.conf can be used in the same manner as before, but deprecated.
If both of object-server.conf with "object-expirer" section and
object-expirer.conf are in a node, only object-server.conf is used.
Object-expirer.conf is used only if all object-server.conf doesn't have
"object-expirer" section.
There are two differences between "object-expirer.conf" style and
"object-server.conf" style.
The first difference is `dequeue_from_legacy` default value.
`dequeue_from_legacy` defines task queue mode. In "object-expirer.conf"
style, the default mode is legacy queue. In "object-server.conf" style,
the default mode is general queue. But general mode means no-op mode
for now, because general task queue is not implemented yet.
The second difference is internal client config. In "object-expirer.conf"
style, config file of internal client is the object-expirer.conf itself.
In "object-server.conf" style, config file of internal client is
another file.
[1]: https://review.openstack.org/#/c/517389/
Co-Authored-By: Matthew Oliver <matt@oliver.net.au>
Change-Id: Ib21568f9b9d8547da87a99d65ae73a550e9c3230
443f029a58