force master housekeeping after a db upgrade

[tardyp]

attempt at fixing the nine.b.net master

[sa2ajj]

Traceback (most recent call last):
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/Twisted-14.0.2-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 1099, in _inlineCallbacks
result = g.send(result)
File "/home/travis/build/buildbot/buildbot/master/buildbot/scripts/upgrade_master.py", line 160, in upgradeDatabase
yield db.masters.setAllMastersActiveLongTimeAgo()
File "/home/travis/build/buildbot/buildbot/master/buildbot/db/masters.py", line 99, in setAllMastersActiveLongTimeAgo
return self.db.pool.do(thd)
exceptions.AttributeError: 'NoneType' object has no attribute 'do'
buildbot.test.unit.test_scripts_upgrade_master.TestUpgradeMasterFunctions.test_upgradeDatabase

[tardyp]

I did not realize it was in travis...

I just fixed that test