BUG/MEDIUM: stream: Fix a possible freeze during a forced shut on a stream

BUG/MEDIUM: stream: Fix a possible freeze during a forced shut on a stream

When a forced shutdown is performed on a stream, it is possible to freeze it
infinitly because it is performed in an unexpected way from process_stream()
point of view, especially when the stream is waiting for a server
connection. The events sequence is a bit complex but at the end the stream
remains blocked in turn-around state and no event are trriggered to unblock
it.

By trying to fix the issue, we considered it was safer to rethink the
feature. The idea is to quickly shutdown a stream to release resources. For
instance to be able to delete a server. So, instead of scheduling a
shutdown, it is more efficient to trigger an error and detach the stream
from the server, if neecessary. The same code than the one used to deal with
connection errors in back_handle_st_cer() is used.

This patch must be slowly backported as far as 2.6.

(cherry picked from commit 51611a5b702e6dbf2e5ac56cbcef211326414282)
Signed-off-by: Aurelien DARRAGON <adarragon@haproxy.com>
(cherry picked from commit bf7dfa488dc3bf830179f13e1262386735a4be91)
Signed-off-by: Aurelien DARRAGON <adarragon@haproxy.com>