Fix flaky unit test in engine
Fix flaky unit test in engine

TestGetTaskByArn and TestMetadataFileUpdatedAgentRestart sometimes can
be flaky due to missing docker api call, as there is no way to stop the
engine from procssing the task. By modifying the desired/known status of
the container/task to reduce this calls.

kiranmeduri/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,aws/amazon-ecs-agent,aws/amazon-ecs-agent,aws/amazon-ecs-agent,swipely/amazon-ecs-agent,aws/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,swipely/amazon-ecs-agent,swipely/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,swipely/amazon-ecs-agent