jsonschema should have tests

[AkihiroSuda]

Can we have a test? What happens when this is out of the sync with the YAML struct definition?

Originally posted by @AkihiroSuda in #2306 (comment)

[afbjorklund]

Now the generation of the schema will fail, if the result doesn't match the default yaml

e.g.

- at '/mountTypesUnsupported': got null, want array 

(if removing the "nullable", like when it was added)