LB node removal minor refactor

Refactored removal of LB node by checking 422 body in errback since
content is acquired inside check_success. This seems a little more
cleaner than earlier
Non-422 failure returns

This will allow non-422 failures to propogate up when checking for
deleted LB.
Merge pull request #565 from rackerlabs/lb_delete_refactor

LB node removal minor refactor