By default, buildbot will attempt to start builds on builders in order from the
builder with the oldest pending request to the newest. This behaviour can be
customized with the c['prioritizeBuilders'] configuration key. 
This key specifies a function which is called with two arguments: a
BuildMaster and a list of Builder objects. It
should return a list of Builder objects in the desired order. 
It may also remove items from the list if builds should not be started
on those builders.
     def prioritizeBuilders(buildmaster, builders):
         """Prioritize builders.  'finalRelease' builds have the highest
         priority, so they should be built before running tests, or
         creating builds."""
         builderPriorities = {
             "finalRelease": 0,
             "test": 1,
             "build": 2,
         }
         builders.sort(key=lambda b: builderPriorities.get(b.name, 0))
         return builders
     
     c['prioritizeBuilders'] = prioritizeBuilders