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/leave_unjoined_chan.py

@@ -0,0 +1,17 @@
+from scenarios import *
+
+scenario = (
+    sequences.handshake(),
+    send_stanza("<presence from='{jid_one}/{resource_one}' to='#foo%{irc_server_one}/{nick_one}' />"),
+    sequences.connection("irc.localhost", '{jid_one}/{resource_one}'),
+    expect_stanza("/message"),
+    expect_stanza("/presence"),
+    expect_stanza("/message"),
+
+    send_stanza("<presence from='{jid_two}/{resource_two}' to='#foo%{irc_server_one}/{nick_one}' />"),
+    sequences.connection_begin("irc.localhost", '{jid_two}/{resource_two}'),
+
+    expect_stanza("/message[@to='{jid_two}/{resource_two}'][@type='chat']/body[text()='irc.localhost: {nick_one}: Nickname is already in use.']"),
+    expect_stanza("/presence[@type='error']/error[@type='cancel'][@code='409']/stanza:conflict"),
+    send_stanza("<presence from='{jid_two}/{resource_two}' to='#foo%{irc_server_one}/{nick_one}' type='unavailable' />")
+)