Documents should not be labeled empty unless they're actually empty

[ian-howell]

Running kubeval against https://raw.githubusercontent.com/instrumenta/kubeval/master/fixtures/multi_invalid.yaml currently gives the following output:

The document fixtures/multi_valid.yaml contains a valid Service
The document fixtures/multi_valid.yaml contains a valid ReplicationController
The document fixtures/multi_valid.yaml contains a valid Service
The document fixtures/multi_valid.yaml contains a valid ReplicationController
The document fixtures/multi_valid.yaml contains a valid Service
The document fixtures/multi_valid.yaml contains a valid ReplicationController
The document fixtures/multi_valid.yaml is empty
The document fixtures/multi_valid.yaml is empty

This output is a bit misleading; kubeval should not report that a non-empty file is empty. Perhaps it makes more sense to state that

The file fixtures/multi_valid.yaml contains an empty YAML document