s3 and swift resources don't upcall in validate

[Thomas Herve]

Both S3Bucket and SwiftContainer contain (useless) validate methods method which don't call Resource.validate, thus not validating properties when doing a Stack.validate. It doesn't create a big problem because we do an additional properties.validate when actually creating the resource, but making the call earlier gives a better error.

Those methods should be removed as they don't provide any value (we already conditionally register them).

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/62394