[ECS] Add support for GPU with Docker 19.03

### Summary
Docker 19.03 now has built-in support for GPU, there is no need to specify an alternate runtime. However, at run time, `--gpus all` or a specific set of GPUs needs to be passed as an argument and it can't be done with dockerd config.

### Description
Without `--gpus all`
```
$ docker run --rm nvidia/cuda:10.1-base nvidia-smi
docker: Error response from daemon: OCI runtime create failed: container_linux.go:345: starting container process caused "exec: \"nvidia-smi\": executable file not found in $PATH": unknown.
```
With `--gpus all`
```
$ docker run --gpus all --runtime runc --rm nvidia/cuda:10.1-base nvidia-smi
Thu Aug 29 13:54:36 2019
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 418.87.00 Driver Version: 418.87.00 CUDA Version: 10.1 |
|-------------------------------+----------------------+----------------------+
| GPU Name Persistence-M| Bus-Id Disp.A | Volatile Uncorr. ECC |
| Fan Temp Perf Pwr:Usage/Cap| Memory-Usage | GPU-Util Compute M. |
|===============================+======================+======================|
| 0 Tesla K80 On | 00000000:00:0F.0 Off | 0 |
| N/A 35C P8 26W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 1 Tesla K80 On | 00000000:00:10.0 Off | 0 |
| N/A 32C P8 29W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 2 Tesla K80 On | 00000000:00:11.0 Off | 0 |
| N/A 40C P8 27W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 3 Tesla K80 On | 00000000:00:12.0 Off | 0 |
| N/A 35C P8 29W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 4 Tesla K80 On | 00000000:00:13.0 Off | 0 |
| N/A 36C P8 26W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 5 Tesla K80 On | 00000000:00:14.0 Off | 0 |
| N/A 34C P8 30W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 6 Tesla K80 On | 00000000:00:15.0 Off | 0 |
| N/A 40C P8 26W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 7 Tesla K80 On | 00000000:00:16.0 Off | 0 |
| N/A 33C P8 29W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 8 Tesla K80 On | 00000000:00:17.0 Off | 0 |
| N/A 36C P8 26W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 9 Tesla K80 On | 00000000:00:18.0 Off | 0 |
| N/A 31C P8 30W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 10 Tesla K80 On | 00000000:00:19.0 Off | 0 |
| N/A 37C P8 26W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 11 Tesla K80 On | 00000000:00:1A.0 Off | 0 |
| N/A 33C P8 29W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 12 Tesla K80 On | 00000000:00:1B.0 Off | 0 |
| N/A 38C P8 26W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 13 Tesla K80 On | 00000000:00:1C.0 Off | 0 |
| N/A 34C P8 32W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 14 Tesla K80 On | 00000000:00:1D.0 Off | 0 |
| N/A 39C P8 27W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 15 Tesla K80 On | 00000000:00:1E.0 Off | 0 |
| N/A 34C P8 30W / 149W | 0MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+

+-----------------------------------------------------------------------------+
| Processes: GPU Memory |
| GPU PID Type Process name Usage |
|=============================================================================|
| No running processes found |
+-----------------------------------------------------------------------------+
```

### Expected Behavior
Containers with GPU requirements should start

### Observed Behavior

### Environment Details
```
$ docker info
Client:
Debug Mode: false

Server:
Containers: 2
Running: 1
Paused: 0
Stopped: 1
Images: 4
Server Version: 19.03.1
Storage Driver: overlay2
Backing Filesystem: xfs
Supports d_type: true
Native Overlay Diff: true
Logging Driver: splunk
Cgroup Driver: cgroupfs
Plugins:
Volume: local
Network: bridge host ipvlan macvlan null overlay
Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 894b81a4b802e4eb2a91d1ce216b8817763c29fb
runc version: 425e105d5a03fabd737a126ad93d62a9eeede87f
init version: fec3683
Security Options:
seccomp
Profile: default
Kernel Version: 3.10.0-957.27.2.el7.x86_64
Operating System: CentOS Linux 7 (Core)
OSType: linux
Architecture: x86_64
CPUs: 64
Total Memory: 720.3GiB
Name: ip-10-45-8-153.us-west-2.compute.internal
ID: GA4Z:BCED:2FQG:AUKO:KUAX:7X5W:SBAR:NWB3:IHCH:6HQN:TIFW:PLOB
Docker Root Dir: /var/lib/docker
Debug Mode: true
File Descriptors: 31
Goroutines: 51
System Time: 2019-08-29T13:55:51.172917082Z
EventsListeners: 0
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
127.0.0.0/8
Live Restore Enabled: true
```
```
$ curl http://localhost:51678/v1/metadata
{"Cluster":"BATCHCLUSTER_Batch_0d2792a4-22a0-37e9-8e8a-5e8b68c1be17","ContainerInstanceArn":"arn:aws:ecs:us-west-2::container-instance/BATCHCLUSTER_Batch_0d2792a4-22a0-37e9-8e8a-5e8b68c1be17/50e649e34b83423189684b82669a1cea","Version":"Amazon ECS Agent - v1.30.0 (02ff320c)"}
```

### Supporting Log Snippets
Logs can be provided on request.

No repository files, tests, or implementation entry points are named. Start by reviewing the ECS task definition and Docker 19.03 GPU requirements described in the issue, then define how GPU selection should be represented and verified so containers with GPU requirements start successfully.

Written by the indexing model from the issue text.