Allow Certificate ARNs to be used for targeting

[zpatrick]

What does this pull request do? closes #491

How should this be tested? Manually with both terraform and the cli

Checklist

• [x] Unit tests
• [x] Documentation (if applicable)

[zpatrick]

testing output:

$ l0 loadbalancer create --certificate "arn:aws:acm:us-west-2:123:certificate/e3dfjd920-9ac2-4bb0-91e1-b2sf5e971" --port 443:443/https dev test2
LOADBALANCER ID  LOADBALANCER NAME  ENVIRONMENT  SERVICE  PORTS          PUBLIC  URL
test2091f4b7     test2              dev                   443:443/HTTPS  true

$ l0 loadbalancer get test2
LOADBALANCER ID  LOADBALANCER NAME  ENVIRONMENT  SERVICE  PORTS          PUBLIC  URL
test2091f4b7     test2              dev                   443:443/HTTPS  true    l0-zpatrick-test2091f4b7-123.us-west-2.elb.amazonaws.com

$ l0 -o json loadbalancer get test2
[
    {
        "environment_id": "dev0abe87008",
        "environment_name": "dev",
        "health_check": {
            "target": "TCP:80",
            "interval": 30,
            "timeout": 5,
            "healthy_threshold": 2,
            "unhealthy_threshold": 2
        },
        "is_public": true,
        "load_balancer_id": "test2091f4b7",
        "load_balancer_name": "test2",
        "ports": [
            {
                "certificate_name": "efs920-9ac2-4bbdf1e1-b239fse971",
                "certificate_arn": "",
                "container_port": 443,
                "host_port": 443,
                "protocol": "HTTPS"
            }
        ],
        "service_id": "",
        "service_name": "",
        "url": "l0-zpatrick-test2091f4b7-123.us-west-2.elb.amazonaws.com"
    }

[zpatrick]

@tlake: I did update the docs; did you miss that or are you saying it need to be called out more?

[tlake]

@zpatrick just a thought about being more explicit regarding IAM/ACM, that's all. Maybe it's not necessary

[jparsons04]

Manually tested a simple terraform structure with 2 LBs, one with a listener with an IAM cert and one with a port with an ACM cert and it built successfully.