fix interrupt()

can't interrupt with things to interrupt. this is technically duplicated
information but keeping parts of the code close to Trigger seems useful.

buildbot_nix/__init__.py

@@ -71,6 +71,7 @@ class BuildTrigger(steps.BuildStep):
         self._result_list = []
         self.ended = False
         self.waitForFinishDeferred = None
+        self.brids = []
         self.description = f"building {len(jobs)} hydra jobs"
         super().__init__(**kwargs)
 
@@ -220,6 +221,7 @@ class BuildTrigger(steps.BuildStep):
                     url = getURLForBuildrequest(self.master, brid)
                     yield self.addURL(f"{scheduler.name} #{brid}", url)
                     self._add_results(brid)
+                    self.brids.append(brid)
             print('Waiting..')
             wait_for_next = defer.DeferredList([results for _, _, results in scheduled], fireOnOneCallback = True, fireOnOneErrback=True)
             self.waitForFinishDeferred = wait_for_next