Fix session logout

There were 2 issues with session logouts, one is that the logout_cookie
was checked and acted on in the wrong place, the other is that the wrong
value was set in the IPASESSION header.

Fixes https://fedorahosted.org/freeipa/ticket/6685

Signed-off-by: Simo Sorce <simo@redhat.com>
Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>

ipaserver/plugins/session.py

@@ -23,6 +23,6 @@ class session_logout(Command):
         else:
             delattr(context, 'ccache_name')
 
-        setattr(context, 'logout_cookie', '')
+        setattr(context, 'logout_cookie', 'MagBearerToken=')
 
         return dict(result=None)