Update controller to cleanup tokens from auth method

[pglass]

Changes proposed in this PR:

This updates the ACL controller to cleanup tokens created by the auth method. The controller's reconcile operation now tracks tasks by task id. It parses the JSON formatted metadata from each ACL token description to determine the task id which created the token. Tokens for which there is no longer an ECS task running are deleted.

This PR also removes the controller's "old" behavior of managing tokens based on service names. The controller no longer creates any tokens, and is only responsible for cleaning up tokens created from a consul login command.

In order for the controller to cleanup a token, the token must have been created with metadata when running the consul login command, which indicates the task id and cluster:

consul login \
    -meta consul.hashicorp.com/task-id=123456 \
    -meta consul.hashicorp.com/cluster=<clusterARN> \
   ...

When the token is created, the metadata is placed in the token description as a JSON string:

AccessorID:       00000000-0000-c962-66c1-d6a3345df4f9
SecretID:         00000000-0000-2663-f30a-e76300fdae8e
Partition:        default
Namespace:        test-ns
Description:      token created via login: {"consul.hashicorp.com/cluster":"<clusterARN>","consul.hashicorp.com/task-id":"123456"}
...

This updates the controller to consistently use the full cluster ARN. The task metadata has a Cluster field, which is the cluster ARN on Fargate but is only the cluster name on EC2.

How I've tested this PR:

• Unit tests
• Acceptance tests in Switch to the auth method terraform-aws-consul-ecs#107

How I expect reviewers to test this PR:

Checklist:

• Tests added
• CHANGELOG entry added

[erichaberkorn]

This ends up being a breaking change, doesn't it?