use a less confusing builder name when reporting on buildsets

This also avoids interploating the reason, which can contain newlines.

master/buildbot/status/mail.py

@@ -477,8 +477,7 @@ def _gotBuilds(self, res, buildset):
                     builds.append(build)
 
         if builds:
-            self.buildMessage("Buildset Complete: " + buildset['reason'], builds,
-                              buildset['results'])
+            self.buildMessage("(whole buildset)", builds, buildset['results'])
 
     def _gotBuildRequests(self, breqs, buildset):
         dl = []