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/basic_subscribe_unsubscribe.py

@@ -0,0 +1,23 @@
+from scenarios import *
+
+scenario = (
+    sequences.handshake(),
+
+    # Mutual subscription exchange
+    send_stanza("<presence from='{jid_one}' to='{biboumi_host}' type='subscribe' id='subid1' />"),
+    expect_stanza("/presence[@type='subscribed'][@id='subid1']"),
+
+    # Get the current presence of the biboumi gateway
+    expect_stanza("/presence"),
+
+    expect_stanza("/presence[@type='subscribe']"),
+    send_stanza("<presence from='{jid_one}' to='{biboumi_host}' type='subscribed' />"),
+
+    # Unsubscribe
+    send_stanza("<presence from='{jid_one}' to='{biboumi_host}' type='unsubscribe' id='unsubid1' />"),
+    expect_stanza("/presence[@type='unavailable']"),
+    expect_stanza("/presence[@type='unsubscribed']"),
+    expect_stanza("/presence[@type='unsubscribe']"),
+    send_stanza("<presence from='{jid_one}' to='{biboumi_host}' type='unavailable' />"),
+    send_stanza("<presence from='{jid_one}' to='{biboumi_host}' type='unsubscribed' />"),
+)