Raise BadRequest when updating 'personality'

Updating booted server instance through server PUT API call with
'personality' property set is not returning 'Bad Request', although the
property is not allowed to be updated once the instance is booted.

This fixes the described problem.

Fixes bug #1032546

Change-Id: Ia086f5ea5176640a9916a3ba42c79d4d5944ce76
Merge "Raise BadRequest when updating 'personality'"