ReST API: Return 400 for malformed JSON input
ReST API: Return 400 for malformed JSON input

Previously we had an unhandled exception that resulted in a 500 (Internal
Server Error) result and a stack trace when an invalid JSON file was
submitted in a POST/PUT request. Change to catching the exception and
returning a 400 (Bad Request) result.

bug 1102391

Change-Id: I7dde33ae732d9addbf988b1d36d4f06eacb634bf
Signed-off-by: Zane Bitter <1899fff8e7db19a598ee9d835aa1a232f82ea264@redhat.com>

steveb/heat,redhat-openstack/heat,Triv90/Heat,cwolferh/heat-scratch,steveb/heat,rdo-management/heat,openstack/heat,srznew/heat,pshchelo/heat,citrix-openstack-build/heat,Triv90/Heat,varunarya10/heat,maestro-hybrid-cloud/heat,cryptickp/heat,dims/heat,openstack/heat,jasondunsmore/heat,dims/heat,maestro-hybrid-cloud/heat,rdo-management/heat,pshchelo/heat,ntt-sic/heat,citrix-openstack-build/heat,NeCTAR-RC/heat,noironetworks/heat,dragorosson/heat,cryptickp/heat,rh-s/heat,Triv90/Heat,ntt-sic/heat,jasondunsmore/heat,srznew/heat,gonzolino/heat,miguelgrinberg/heat,redhat-openstack/heat,dragorosson/heat,varunarya10/heat,rickerc/heat_audit,NeCTAR-RC/heat,rh-s/heat,gonzolino/heat,pratikmallya/heat,cwolferh/heat-scratch,rickerc/heat_audit,takeshineshiro/heat,pratikmallya/heat,JioCloud/heat,miguelgrinberg/heat,noironetworks/heat,JioCloud/heat,takeshineshiro/heat