validating schema in discovery mode

[nick-mccoy]

Added write_catalog function

[mdelaurentis]

Code looks good. Please see the one comment on additionalProperties.

What does it look like to the user when the tap provides a schema that fails validation? I would suggest adding a test for that case. You can use the assertRaisesRegex context manager, as documented here: https://docs.python.org/3/library/unittest.html#unittest.TestCase.assertRaisesRegex.

Like:

with self.assertRaisesRegex(ValueError, "Some pattern you want the message to match):
    do(some_stuff)

[mdelaurentis]

I think you might want to add "additionalProperties": false here and in the other nested object in this schema. If you don't the validator will allow objects with other properties. I guess it depends on how strict we want to be in this validation. @cmerrick what are your thoughts on that?

[mdelaurentis]

@nick-mccoy tests are failing. It's a pretty trivial issue, just pylint complaining about whitespace.