The mocked response for ECS RegisterTaskDefinition has drifted from what
actually returns when run against a real ECS endpoint. I created a
minimal task definition for both EC2:
```
>>> ecs.register_task_definition(
family="moto",
containerDefinitions=[
{
"name": "hello_world",
"image": "hello-world:latest",
"memory": 400
}
]
)["taskDefinition"]
{'taskDefinitionArn': 'arn:aws:ecs:us-east-1:************:task-definition/moto:1',
'containerDefinitions': [{'name': 'hello_world',
'image': 'hello-world:latest',
'cpu': 0,
'memory': 400,
'portMappings': [],
'essential': True,
'environment': [],
'mountPoints': [],
'volumesFrom': []}],
'family': 'moto',
'revision': 1,
'volumes': [],
'status': 'ACTIVE',
'placementConstraints': [],
'compatibilities': ['EC2']}
```
and FARGATE:
```
>>> ecs.register_task_definition(
family="moto",
containerDefinitions=[
{
"name": "hello_world",
"image": "hello-world:latest",
"memory": 400
}
],
requiresCompatibilities=["FARGATE"],
networkMode="awsvpc",
cpu="256",
memory="512"
)["taskDefinition"]
{'taskDefinitionArn': 'arn:aws:ecs:us-east-1:************:task-definition/moto:2',
'containerDefinitions': [{'name': 'hello_world',
'image': 'hello-world:latest',
'cpu': 0,
'memory': 400,
'portMappings': [],
'essential': True,
'environment': [],
'mountPoints': [],
'volumesFrom': []}],
'family': 'moto',
'networkMode': 'awsvpc',
'revision': 2,
'volumes': [],
'status': 'ACTIVE',
'requiresAttributes': [{'name': 'com.amazonaws.ecs.capability.docker-remote-api.1.18'},
{'name': 'ecs.capability.task-eni'}],
'placementConstraints': [],
'compatibilities': ['EC2', 'FARGATE'],
'requiresCompatibilities': ['FARGATE'],
'cpu': '256',
'memory': '512'}
```
This change adds several default keys to the task based on those two
real responses and the AWS documentation:
https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_RegisterTaskDefinition.html
The mock still doesn't match the real response exactly but it's much
closer than it was before.
