dockerImageId can not be known before dockerFile build

I’m having an issue with the dockerFile component of the spec and cwltool implementation.

If I specify a dockerFile, the build system must execute before the image hash can be known. The human-readable name (repository+tag), can be referenced…but the hash can’t be known until the build is complete.

Perhaps dockerImageId should be called dockerName, as the imageId refers to something specific which is not the human-readable name. Reference: https://docs.docker.com/engine/reference/commandline/images/