Split all the e2e tests in their own files

Some duplication is avoided, but most importantly: it’s much much cleaner,
easier to find, functions have been cleaned up (functools.partial usages are
now hidden), etc.

tests/end_to_end/scenarios/notices.py

@@ -0,0 +1,10 @@
+from scenarios import *
+
+import scenarios.simple_channel_join
+
+scenario = (
+    scenarios.simple_channel_join.scenario,
+
+    send_stanza("<message from='{jid_one}/{resource_one}' to='{irc_server_one}' type='chat'><body>NOTICE {nick_one} :[#foo] Hello in a notice.</body></message>"),
+    expect_stanza("/message[@from='#foo%{irc_server_one}/{nick_one}'][@type='groupchat']/body[text()='[notice] [#foo] Hello in a notice.']"),
+)