When building in Yocto using a whitespace in MENDER_ARTIFACT_NAME, the build succeeds but deployments using this Artifact do not work. See the relevant mailing list topic for details.
As there could be other side-effects of allowing whitespace in the Artifact name, I propose to disallow it and failing the build if there is whitespace. We should also have a sanity check on the length (e.g. 60 chars).
We also need to update the docs with any restrictions, most notably the variable reference: https://docs.mender.io/1.1/artifacts/variables#mender_artifact_name