Restrict jsonschema to <2 for now

blueprint nova-api-validation-fw(Ieba96718264ad2ddfba63b65425f7e5bbb8606a9)
uses internal functions of jsonschema>=1.0.0,<2. These functions has been
changed since jsonschema 2.0.0.

Current JSON-Schema specification is draft-4, and it will be changed in
the future. So for now, this patch restricts jsonschema <2.
When full JSON-Schema specification will be implemented or we need more the
features of the latest jsonschema library, this restrictions must be changed.

Change-Id: I20c77f20cf26b19cd7293a4315d9ffda6b8b45e5
Merge "Restrict jsonschema to <2 for now"