Fix jsonschema>=2.4.0 message assertion

The jsonschema 2.4.0 release slightly changed some of the error messages
that are provided when validation fails. This patch updates the unit tests to
expect the proper string and avoid failing as a result by using regex
(.0)? instead of specific value.

Change-Id: Ifd41147fd6157038b102c78144d1f6cb16cc25e6
Closes-bug: #1359284