e2e: Implicitely include the handshake in all tests

Instead of having to write it manually everytime

tests/end_to_end/scenarios/list_adhoc.py

@@ -1,7 +1,6 @@
 from scenarios import *
 
 scenario = (
-    sequences.handshake(),
     send_stanza("<iq type='get' id='idwhatever' from='{jid_one}/{resource_one}' to='{biboumi_host}'><query xmlns='http://jabber.org/protocol/disco#items' node='http://jabber.org/protocol/commands' /></iq>"),
     expect_stanza("/iq[@type='result']/disco_items:query[@node='http://jabber.org/protocol/commands']",
                   "/iq/disco_items:query/disco_items:item[@node='configure']",