e2e: Implicitely include the handshake in all tests

Instead of having to write it manually everytime

tests/end_to_end/scenarios/fixed_muc_disco_info.py

@@ -3,8 +3,6 @@ from scenarios import *
 conf = 'fixed_server'
 
 scenario = (
-    sequences.handshake(),
-    
     send_stanza("<iq from='{jid_one}/{resource_one}' to='#foo@{biboumi_host}' id='1' type='get'><query xmlns='http://jabber.org/protocol/disco#info'/></iq>"),
     expect_stanza("/iq[@from='#foo@{biboumi_host}'][@to='{jid_one}/{resource_one}'][@type='result']/disco_info:query",
                   "/iq[@type='result']/disco_info:query/disco_info:identity[@category='conference'][@type='irc'][@name='#foo on {irc_host_one}']",