e2e: Implicitely include the handshake in all tests

Instead of having to write it manually everytime

tests/end_to_end/scenarios/irc_channel_configure_fixed.py

@@ -3,7 +3,6 @@ from scenarios import *
 conf = 'fixed_server'
 
 scenario = (
-    sequences.handshake(),
     send_stanza("<iq type='set' id='id1' from='{jid_one}/{resource_one}' to='#foo@{biboumi_host}'><command xmlns='http://jabber.org/protocol/commands' node='configure' action='execute' /></iq>"),
     expect_stanza("/iq[@type='result']/commands:command[@node='configure'][@sessionid][@status='executing']",
                   "/iq/commands:command/dataform:x[@type='form']/dataform:field[@type='text-single'][@var='encoding_in']",