Support throttling for ECS API

[karaluh]

We're deploying multiple services in parallel with --no-wait option, and are occasionally hit with a throttling exception:

[ERROR] FAILED. failed to register task definition: operation error ECS: RegisterTaskDefinition, exceeded maximum number of attempts, 3, https response error StatusCode: 400, RequestID: 45830576-5b7d-4237-9045-f12eb8b6e4f2, api error ThrottlingException: Rate exceeded

Theoretically, it is possible to request quota increase, but we tried it and AWS engineers didn't really want to do this. More info: https://docs.aws.amazon.com/AmazonECS/latest/APIReference/request-throttling.html

[fujiwara]

@karaluh To solve this, we should increase the retrying count to call ECS API.
I'll try it later.