df: types: Add tests for Input subspec functionality

[johnandersen777]

https://codecov.io/gh/intel/dffml/src/master/dffml/df/types.py#L289

We should also have else statements after value = definition.spec(**value) and line 296, in the body of the else raise SpecValidationError, make sure we have coverage on those errors as well with self.assertRaises (and self.assertRaisesRegex if needed)

[johnandersen777]

We have coverage on this now