* provider/aws: test empty plan with sns_topic policy with random order
If we setup a sns_topic policy with a policy with a different order
to the one set by the AWS API, terraform plan will be not empty between
runs.
* provider/aws: normalize json policy for sns topic
For the policy attribute of the resource aws_sns_topic, AWS returns the policy
in JSON format with the fields in a different order.
If we store and compare the values without normalizing, terraform
will unnecesary trigger and update of the resource.
To avoid that, we must add a normalization function in the StateFunc of
the policy attribute and also when we read the attribute from AWS.
Mitchell Hashimoto