Handle ConnectionResetError from rabbitmq.

As seen in
https://ubuntu-archive-team.ubuntu.com/proposed-migration/log/noble/2024-04-01/12:52:27.log

Having an entire britney run bail because of a connection reset is a bad
outcome!

Instead, catch this exception and avoid adding the test in question to the
list of queued tests (we can pick it up on the next run).

Possibly we should do more clever handling of a ConnectionResetError such as
reconnecting, but this is a minimum fix that will stop britney from aborting.

britney2/policies/autopkgtest.py

@@ -1118,9 +1118,11 @@ class AutopkgtestPolicy(BasePolicy):
 
         If huge is true, then the request will be put into the -huge instead of
         normal queue.
+
+        Return True if successfully queued, False if not.
         '''
         if self.options.dry_run or self.dry_run:
-            return
+            return True
 
         params = {'triggers': triggers}
         if self.options.adt_ppas:
@@ -1135,9 +1137,12 @@ class AutopkgtestPolicy(BasePolicy):
         if self.amqp_channel:
             import amqplib.client_0_8 as amqp
             params = json.dumps(params)
+            try:
                 self.amqp_channel.basic_publish(amqp.Message(src + '\n' + params,
                                                              delivery_mode=2),  # persistent
                                                 routing_key=qname)
+            except ConnectionResetError:
+                return False
         else:
             # for file-based submission, triggers are space separated
             params['triggers'] = [' '.join(params['triggers'])]
@@ -1145,6 +1150,7 @@ class AutopkgtestPolicy(BasePolicy):
             assert self.amqp_file
             with open(self.amqp_file, 'a') as f:
                 f.write('%s:%s %s\n' % (qname, src, params))
+        return True
 
     def pkg_test_request(self, src, arch, full_triggers, huge=False):
         '''Request one package test for one particular trigger
@@ -1214,10 +1220,11 @@ class AutopkgtestPolicy(BasePolicy):
             self.logger.info('Test %s/%s for %s is already pending, not queueing', src, arch, trigger)
         else:
             self.logger.info('Requesting %s autopkgtest on %s to verify %s', src, arch, trigger)
+            if self.send_test_request(src, arch, full_triggers, huge=huge):
+                # save pending.json right away, so that we don't re-request
+                # if britney crashes
                 arch_list.append(arch)
                 arch_list.sort()
-            self.send_test_request(src, arch, full_triggers, huge=huge)
-            # save pending.json right away, so that we don't re-request if britney crashes
                 self.save_pending_json()
 
     def result_in_baseline(self, src, arch):