This API return error when underlying 'inspect' command
fails. This makes ImagePullCheck to fail as it doesn't expect
runtime.ImageExists to return an error even if image doesn't exist.
Fixed this by returning error nil even when inspect command fails.
Improved runtime tests by using T.Run API:
https://golang.org/pkg/testing/#T.Run
This should improve the test output and make it more visible
which test is doing what.
