[feature] validate logins

[dweomer]

Is this Feature/Enhancement related to an Existing Problem? If so, please describe:

• @bgulla reports that hauler login did not validate the login with the registry, which surprised him

Describe Proposed Solution(s):

• hauler login should attempt to access some protected resource under /v2 at the registry and return non-zero exit code for http 400/500 errors

Describe Possible Alternatives:

Additional Context:

• n/a