Implement slowcgi_timeout() to actually kill the backend bgpctl process.

Implement slowcgi_timeout() to actually kill the backend bgpctl process.
If that succeeds the fcgi session will be terminated the regular way.
If it fails close all fds and finish the request.
Sending a SIGTERM to a read only bgpctl process should be fine at any point.
Also reduce the timeout to 30sec. This is not long enough to dump a full
rib but nobody should do that.
OK tb@