RFE: `upslog` might do well to reuse `libupsclient` connections when logging multiple devices from the same server

[jimklimov]

Investigated, not a leak but overlooked behavior in test: upslog is used with * to monitor all UPSes on a server, so each client process established that many libupsclient connections.

It may be or not be reasonable to have an upslog monitoring multiple devices from the same server re-use the connection (see #1639, #2756 etc.), but that is a separate issue.

Originally posted by @jimklimov in #3366