checkAllPads: Increase performance/resilience
checkAllPads: Increase performance/resilience

Performance: Don't preload pads. Check for pool only once per pad.
Resilience: Handle missing revision.
lpagliari/etherpad-lite,aptivate/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,cloudfoundry-community/etherpad-lite-cf,aptivate/etherpad-lite,lpagliari/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,aptivate/etherpad-lite,ether/etherpad-lite,storytouch/etherpad-lite,University-of-Potsdam-MM/etherpad-lite,aptivate/etherpad-lite,ether/etherpad-lite,joequant/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,University-of-Potsdam-MM/etherpad-lite,storytouch/etherpad-lite,University-of-Potsdam-MM/etherpad-lite,ether/etherpad-lite,lpagliari/etherpad-lite,joequant/etherpad-lite,lpagliari/etherpad-lite,storytouch/etherpad-lite,joequant/etherpad-lite,University-of-Potsdam-MM/etherpad-lite,joequant/etherpad-lite