If you're running servers_per_port > 0 and threads_per_disk = 0 (as it
should be with servers_per_port on), each object-server process will
have 20 IO threads waiting around to service eventlet.tpool
calls. This is far too many; with servers_per_port, there's no real
benefit to having so many IO threads.
This commit makes it so that, when servers_per_port > 0, each object
server defaults to having one main thread and one IO thread.
Also, eventlet's tpool size is now configurable via the object-server
config file. If a tpool size is set, that's what we'll use regardless
of servers_per_port. This allows operators with an excess of threads
to remove some regardless of servers_per_port.
Change-Id: I8f8914b7e70f2510393eb7c5e6be9708631ac027
Closes-Bug: 1554233
d9c4913e3b