Raise ValueError on empty argument to inspect_{container,image}() methods.

[posita]

Fix #602. Raise ValueError on empty argument to inspect_{container,image}() methods.

[posita]

This if isinstance ... block wasn't part of the original issue, but is included to provide consistency with the inspect_container() method.

[shin-]

This would be better done in the check_resource decorator.

[posita]

@shin, I've moved the check to @check_resource as you suggest (and squashed commits). Tests pass. Are you sure this won't have detrimental side effects elsewhere?

[posita]

This isn't required to fix #602, but the change is make this method consistent with inspect_container.

@shin, incidentally, this also looks like a good candidate for inclusion in @check_resource. Similar checks are littered throughout client.py (but still missing from some methods). See my raise-on-inspect-empty-string-602-with-id-resolution-in-check-resource branch. (Tests pass.)

[posita]

BTW, if this PR looks good for merge as-is, I can propose another that moves code like the following into @check_resource (see my line note on docker/client.py above):

    if isinstance(..., dict):
        ... = ....get('Id')

I think those changes are beyond the scope of this PR though.

[shin-]

Thanks!