Fix profile yml error handling

[beckjake]

Fix #816 and add tests. The issue is that when I migrated to the JSON schema validator I tried to preserve too much of the old without really understanding what I was doing. I think the right thing is to move some of the logic into the ValidationException, store the intermediate steps on that object, and do all this regex unpleasantness there to figure out what kind of validation issues we had so we can generate a nice message for the user.

The new validator also seems to sometimes repeat the same errors multiple times so I stripped duplicates.

The new error looks like this (two extra keys, two missing keys):

Encountered an error while reading the project:
Runtime Error
  Invalid arguments passed to "CredentialsValidator" instance: 'schema' is a required property, 'dbname' is a required property, Additional properties are not allowed ('morejunk', 'junk' were unexpected)
Defined profiles:
 - postgres

For more information on configuring profiles, please consult the dbt docs:

https://docs.getdbt.com/docs/configure-your-profile

Encountered an error:
Could not run dbt

Is this obvious enough? Should we somehow try to make it more clear at this point that it's the profile that's probably wrong and not the dbt_project.yml file? The only line that we really can control without this turning into something huge is the Extra project configuration value(s)... line. Is Extra profile configuration value(s)... better? Or even Extra connection configuration value(s) in profile ...?

[cmcarthur]

this looks generally ok, but i'm a little confused by the changes to dbt/exceptions.py. it looks like your changes to api/object.py, coupled with more straightforward rendering of the exception in dbt/project.py, should address the entire issue, right? it looks like you are trying to add another layer of user-friendliness here in dbt/exceptions.py, but i'm not sure that it hits the mark.

let me know what you think. my suggestion is to get rid of that intermediate error message manipulation code in dbt/exceptions.py and then this will be approved

[cmcarthur]

are these messages returned by the json schema validator? is there an api where we can get structured data from the validation instead of strings?

[beckjake]

Sort of. You can get that there are extra properties or that there are missing properties, but the names of those properties are only exposed in the message, which is why I went through all these ugly machinations.

[cmcarthur]

i like the idea of accepting structured data here. have you checked everywhere in the code that uses ValidationException to make sure this is compatible?

this ValidationException is generic across all of dbt -- it applies to other things, like models and schema.yml, etc. so i don't think this is the right place to wire in _causes_from_errors that refers specifically to project configuration.

[beckjake]

Ok, I misunderstood ValidatorException (the validator library) vs ValidationException (dbt). I'll move this stuff out into the APIObject or something