ContainerFactory feature is not compliant with the Vorto model

[konstantina-gramatova]

The current implementation of the ContainerFactory feature does not implement the specified Vorto model in its definition in a compliant manner.

As defined in the model, both create and createWithConfig operations must return the ID of the created container instance:

operations {
        create(.......) returns string "Creates ...."
                createWithConfig(....) returns string "Creates ....."
  }

Currently, the implementation does not return any result and it must be fixed accordingly. Any relevant unit/integration TCs must be updated accordingly as well.