xmlrpc_manager tries to reuse closed connections

[mgrrx]

I found time again to revisit the CLOSE_WAIT. Although most CLOSE_WAIT problems are already fixed, roscpp nodes still have always one port in CLOSE_WAIT. This can be easily reproduced by just starting a roscore. The rosout process then has one port in CLOSE_WAIT.

As already addressed in #371, the xmlrpc server used in rosmaster does not use HTTP/1.1. Activating it still leads to the same behavior as reported back then.
Surprisingly, the xmlrpc_manager in roscpp tries to reuse the connections even if the server replies with HTTP/1.0 and closes the connection. Adding the keep-alive flag to the request doesn't help - the server will always close the connection.

I see three solutions to this problem:

1. Find out why activating HTTP/1.1 in the xmlrpc servers leads to the behavior described in Use HTTP1.1: we get persistent connections for free #371 and fix this issue.
2. Detect that the server responds with HTTP/1.0 and close the connection accordingly.
3. Do not cache any xmlrpc connection in roscpp.

I have a working solution for solution 2 which I'll upload in a bit.

[mgrrx]

1. Is implemented in Use HTTP/1.1 in XMLRPC Server #1287
2. Is implemented in [kinetic] Close sockets when server responds with HTTP/1.0 #1284
3. Is then obsolete

[flixr]

I guess this can be closed as with #1287 merged this doesn't happen anymore in melodic.