Support trust top-level image like "centos" when "library" is configured in "docker.trusted.registries"

There are some missing cases that we need to catch when handling "docker.trusted.registries".

The container-executor.cfg configuration is as follows:

docker.trusted.registries=tangzhankun,ubuntu,centos

It works if run DistrubutedShell with "tangzhankun/tensorflow"

"yarn ... -shell_env YARN_CONTAINER_RUNTIME_TYPE=docker -shell_env YARN_CONTAINER_RUNTIME_DOCKER_IMAGE=tangzhankun/tensorflow

But run a DistrubutedShell job with "centos", "centos[:tagName]", "ubuntu" and "ubuntu[:tagName]" fails:
The error message is like:

"image: centos is not trusted"

We need better handling the above cases.