e2e: Implicitely include the handshake in all tests

Instead of having to write it manually everytime

tests/end_to_end/scenarios/nick_change_in_join.py

@@ -3,7 +3,6 @@ from scenarios import *
 from scenarios.simple_channel_join import expect_self_join_presence
 
 scenario = (
-    sequences.handshake(),
     send_stanza("<presence from='{jid_one}/{resource_one}' to='#foo%{irc_server_one}/{nick_one}' />"),
     sequences.connection(),
     expect_self_join_presence(jid = '{jid_one}/{resource_one}', chan = "#foo", nick = "{nick_one}"),