##### SUMMARY

When using the `ec2_asg` module with `replace_all_instances: yes`, then `wait_for_instances` is effectively ignored. 

I would expect that if `wait_for_instances: no` then it would not wait for instances to complete starting/termination. 


##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
ec2_asg 

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```
ansible 2.9.2
  config file = None
  configured module search path = ['/home/user/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /home/user/.local/lib/python3.7/site-packages/ansible
  executable location = /home/user/.local/bin/ansible
  python version = 3.7.5 (default, Nov 20 2019, 09:21:52) [GCC 9.2.1 20191008]
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
``` 
(empty) 
```

##### OS / ENVIRONMENT
OS: Ubuntu 19.10
Ansible installed via pip3 

##### STEPS TO REPRODUCE
```
- name: Update ASG
  ec2_asg:
    name: "my-asg" 
    launch_config_name: "my-launchconfig"
    min_size: 1       
    max_size:  1
    replace_batch_size: 1
    replace_all_instances: yes
    wait_for_instances: no
```

This will not return successfully until new instance(s) have started, and any existing instance(s) have completed termination. 

If your timeout is not set long enough, then you'll get a 'Waited too long for old instances to terminate' response.  

##### EXPECTED RESULTS

I would expect that it would issue commands to terminate old instances and start new instances, without waiting. 

For those who have to replace in smaller batches than the current `desired_capacity`, then they would need to set `wait_for_instances: yes`.  Perhaps a warning might be in order if `replace_batch_size` is less than `desired_capacity`

##### ACTUAL RESULTS

Playbook output when it takes too long to execute: 

```
TASK [test : Update ASG] ***********************************************************************************************************************************************
fatal: [localhost]: FAILED! => {"changed": false, "msg": "Waited too long for old instances to terminate. Wed Dec 18 12:51:55 2019"}
```
healthy_instances = set()
    as_group = describe_autoscaling_groups(asg_connection, group_name)[0]
    props = get_properties(as_group)
    
    instances = []
    for instance, settings in props['instance_facts'].items():
        if settings['lifecycle_state'] == 'InService' and settings['health_status'] == 'Healthy':
            instances.append(dict(InstanceId=instance))
    module.debug("ASG considers the following instances InService and Healthy: %s" % instances)
    module.debug("ELB instance status:")
    lb_instances = list()
    for lb in as_group.get('LoadBalancerNames'):
        
        
        try:
            lb_instances = describe_instance_health(elb_connection, lb, instances)
        except botocore.exceptions.ClientError as e:
            if e.response['Error']['Code'] == 'InvalidInstance':
                return None
            module.fail_json(msg="Failed to get load balancer.",
                             exception=traceback.format_exc(), **camel_dict_to_snake_dict(e.response))
        except botocore.exceptions.BotoCoreError as e:
            module.fail_json(msg="Failed to get load balancer.",
                             exception=traceback.format_exc())
        for i in lb_instances.get('InstanceStates'):
            if i['State'] == "InService":
                healthy_instances.add(i['InstanceId'])
            module.debug("ELB Health State %s: %s" % (i['InstanceId'], i['State']))
    return len(healthy_instances)
def tg_healthy(asg_connection, elbv2_connection, group_name):