Support API errors from data models

While the API framework is designed to provide a level of call
validation (using JSON-Schema), the data model may provide additional
validation that may fail.  In these cases, the data model may throw a
DataModelException to pass the appropriate response back to the API caller.

Change-Id: If74c0960f1907fe72b02f2fc465c1a3648559cea
Partial-Bug: #1356619
Merge "Support API errors from data models"