CLB nodes batch addition

Adding nodes in batch. Doing this should reduce network traffic to CLB and reduce 422 PENDING_UPDATE errors. 

This is experimental code written at 1 AM in the night when I was not feeling sleepy. This has not been tested at all. Please do have a look at it. I can write tests after getting 1-2 reviews.
This isn't the first time we've done global stuff to work around the structure of our job execution code (#607).

Would you wanna try to discuss this sometime to figure out how we'd need to refactor the code so we could localize this state?