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/channel_custom_topic.py

@@ -0,0 +1,30 @@
+from scenarios import *
+
+import scenarios.simple_channel_join
+
+scenario = (
+    scenarios.simple_channel_join.scenario,
+
+    # First user sets the topic
+    send_stanza("<message from='{jid_one}/{resource_one}' to='#foo%{irc_server_one}' type='groupchat'><subject>TOPIC TEST</subject></message>"),
+    expect_stanza("/message[@from='#foo%{irc_server_one}/{nick_one}'][@type='groupchat'][@to='{jid_one}/{resource_one}']/subject[text()='TOPIC TEST']"),
+
+    # Second user joins
+    send_stanza("<presence from='{jid_two}/{resource_one}' to='#foo%{irc_server_one}/{nick_two}' />"),
+    sequences.connection("irc.localhost", '{jid_two}/{resource_one}'),
+    expect_unordered(
+        [
+            "/presence[@to='{jid_one}/{resource_one}'][@from='#foo%{irc_server_one}/{nick_two}']/muc_user:x/muc_user:item[@affiliation='none'][@jid='{lower_nick_two}%{irc_server_one}/~{nick_two}@localhost'][@role='participant']"
+        ],
+        [
+            "/presence[@to='{jid_two}/{resource_one}'][@from='#foo%{irc_server_one}/{nick_one}']/muc_user:x/muc_user:item[@affiliation='admin'][@role='moderator']"
+        ],
+        [
+            "/presence[@to='{jid_two}/{resource_one}'][@from='#foo%{irc_server_one}/{nick_two}']/muc_user:x/muc_user:item[@affiliation='none'][@jid='{lower_nick_two}%{irc_server_one}/~{nick_two}@localhost'][@role='participant']",
+            "/presence/muc_user:x/muc_user:status[@code='110']"
+        ],
+        [
+            "/message[@from='#foo%{irc_server_one}/{nick_one}'][@type='groupchat']/subject[text()='TOPIC TEST']"
+        ]
+    )
+)