Merge Feature/task-resource-accounting to dev

[prateekchaudhry]

Summary

This feature implements task resource accounting in agent.

• It removes task serialization where a task would wait for previous stopping tasks before progressing
• It implements a host resource manager which keeps account of tasks which have 'taken' resources on the host. A running task frees resources with host resource manager on emitting it's change of status to STOPPED to ECS backend. Tasks waiting for resources will wait in a queue until enough resources for them become available. Current resources being tracked are cpu, memory, ports (tcp/udp) and number of gpus.

Implementation details

#3684 Host Resource Manager initialization
#3706 Add method to get host resources reserved for a task
#3700 Add host resource manager methods
#3723 Remove task serialization and use host resource manager for task resources
#3741 Add integ tests for task accounting
#3747 Change reconcile/container update order on init and waitForHostResources/emitCurrentStatus order
#3750 Dont consume host resources for tasks getting STOPPED while waiting in waitingTasksQueue

Related Containers Roadmap Issue

aws/containers-roadmap#325

Testing

Manual verification along with unit tests, integ tests and functional tests in the mentioned PRs to check methods and functional behavior

New tests cover the changes:
Yes

Description for the changelog

Add task resource accounting in ECS Agent

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[danehlim]

Discussed and confirmed manual verification done for this PR offline, PR LGTM.