Add litmus test based on the flywheel exchange

[kofalt]

Adds a variant to the test script, that checks all the latest gears in the exchange.

On general principles, if something there fails to validate, there is probably a bug in either the exchange, or, more likely, an in-development schema change.

Example:

Testing bxh-xcede-tools-qa.json...                                           [X]
Testing mri-deface.json...                                                   [X]
Testing fmriprep.json...                                                     [X]
Testing extract-cmrr-physio.json...                                          [X]
Testing hcp-diff.json...                                                     [X]
Testing fsl-fslhd.json...                                                    [X]
Testing sti-qsm-demo.json...                                                 [X]
Testing eeg-classifier.json...                                               [X]
Testing hcp-struct.json...                                                   [X]
...