Business exceptions produce error code 400
Business exceptions produce error code 400

NailgunException descendants now produce http errors with code 400 and
exception text included.

Change-Id: Ic5d230d4a4b92228aae74161c1bcf8e14b2167f3
Closes-Bug: #1592309

stackforge/fuel-web,stackforge/fuel-web,stackforge/fuel-web