921 fix public subnet retrieval

[PacoVK]

What I did Classify VPC subnets and allow Loadbalancer creation in Public subnets only fixes #921 and improves #1064 Related issue

(not mandatory) A picture of a cute animal, if possible in relation with what you did

[komatom]

hmm this is here from February anyone tested this?

[sebtrack]

Any progress with that? #921

[komatom]

This in my case is needed to workaround issue where nfs targets are created in all availability zones, instead of only public ones, where duplicate occurs and whole stack is rollbacked. Happens when you have private networks alongside public ones.