* provider/aws: Add aws_alb data source
This adds the aws_alb data source for getting information on an AWS
Application Load Balancer.
The schema is nearly the same as the resource of the same name, with
most of the resource population logic de-coupled into its own function
so that they can be shared between the resource and data source.
* provider/aws: aws_alb data source language revisions
* Multiple/zero result error slightly updated to be a bit more
specific.
* Fixed relic of the copy of the resource docs (resource -> data
source)
Chris Marchesi