Create Image Localizer

Refer YARN-3854.

Add Docker Image Localizer. The image localizer is part of ResourceLocalizationService. It serves the following purpose:

1. All image localization requests will be served by image localizer.
2. Image localizer initially runs DockerImagesCommand to find all images on the local node.
3. For an image localization request, it executes DockerPullCommand if the image is not present on the local node.
4. It returns the status of image localization by periodically executing DockerImagesCommand on a particular image.

LinuxContainerExecutor is for container operations. DockerImagesCommand is independent of any container. The image localizer acts as a service that will localize docker images and maintain an image cache. Other components can use this to query about the images on the node.