tools/xenstored: close socket connections on error

tools/xenstored: close socket connections on error

On error, don't keep socket connection in ignored state but close them.
When the remote end of a socket is closed, xenstored will flag it as an
error and switch the connection to ignored. But on some OSes (e.g.
NetBSD), poll(2) will return only POLLIN in this case, so sockets in ignored
state will stay open forever in xenstored (and it will loop with CPU 100%
busy).

Fixes: d2fa370d3ef9 ("tools/xenstore: Preserve bad client until they are destroyed")
Signed-off-by: Manuel Bouyer <bouyer@netbsd.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>