oliviassss: Restrict subnet auto-discovery to new LB creation on service side

JobBuild
2129
07-21 20:10
pull-aws-load-balancer-controller-e2e-test 1417998853256253440 1417989049271980032 1417940131221868544
pull-aws-load-balancer-controller-lint 1417998853163978752 1417989049188093952 1417940131129593856
pull-aws-load-balancer-controller-unit-test 1417998853205921792 1417989049230036992 1417940131171536896