e2e: Add a 10s timeout for expect_stanza

Otherwise, if we expect a stanza and biboumi never sends it, we just hang
here.

Now, we display a nice error after 10 seconds, and move on to the next test,
as other failures (xpath doesn’t match) do

tests/end_to_end/__main__.py

@@ -83,6 +83,7 @@ class XMPPComponent(slixmpp.BaseXMPP):
 
         self.scenario = scenario
         self.biboumi = biboumi
+        self.timeout_handler = None
         # A callable, taking a stanza as argument and raising a StanzaError
         # exception if the test should fail.
         self.stanza_checker = None
@@ -96,6 +97,13 @@ class XMPPComponent(slixmpp.BaseXMPP):
         self.scenario.steps = []
         self.failed = True
 
+    def on_timeout(self, xpaths):
+        error_msg = "Timeout while waiting for a stanza that would match the expected xpath(s):"
+        for xpath in xpaths:
+            error_msg += "\n" + xpath
+        self.error(error_msg)
+        self.run_scenario()
+
     def on_end_session(self, _):
         self.loop.stop()
 
@@ -113,6 +121,9 @@ class XMPPComponent(slixmpp.BaseXMPP):
         self.run_scenario()
 
     def run_scenario(self):
+        if self.timeout_handler is not None:
+            self.timeout_handler.cancel()
+            self.timeout_handler = None
         if self.scenario.steps:
             step = self.scenario.steps.pop(0)
             try: