e2e: Implicitely include the handshake in all tests

Instead of having to write it manually everytime

tests/end_to_end/scenarios/configure_bad_value.py

@@ -1,8 +1,6 @@
 from scenarios import *
 
 scenario = (
-    sequences.handshake(),
-
     # Configure the throttle option with an incorrect value
     send_stanza("<iq type='set' id='id1' from='{jid_one}/{resource_one}' to='{irc_server_one}'><command xmlns='http://jabber.org/protocol/commands' node='configure' action='execute' /></iq>"),
     expect_stanza("/iq[@type='result']",