PTFM-8497: fixes for dx describe jobs with resolved JBORs

Summary:
In particular, use additional API calls to ensure that the correct
resolutions are reported (even in cases of flattened arrays, etc.)

Test Plan: added unit test

Reviewers: akislyuk

Reviewed By: akislyuk

Differential Revision: https://phabricator.dnanexus.com/D80