Until know, for scale issues, the creation of some NSX backend resources
for loadbalancing was postpone until the first member creation.
This complicates the code unnecessarily, since the scale issues were
already resolved.
The new code will create the matching backend objects for each
LBaaS/Octavia object upon creation.
In case external vip loadbalancer - the service will be created without an attachement,
which will be added upon member creation.
In addition a DB migration is added to mark as ERROR old incomplete load
balancers.
Depends-on: Ic4e604883a7b1437af995110d2d684c0bd396a52
Change-Id: Ib478c336840c2e441bbaeffe94700a5e267c6bef
dddce2f9fb