Fix wrong log level
Fix wrong log level

If a wrong key_name or image_name is configured in heat template,
"exception" log level is used to report it. This should be the "info"
level.

Change-Id: I79122c22f2278e7c1a4e3daba70c122b78fb9aec
Closes-Bug:#1353328

pshchelo/heat,cryptickp/heat,noironetworks/heat,noironetworks/heat,takeshineshiro/heat,openstack/heat,pratikmallya/heat,rh-s/heat,redhat-openstack/heat,steveb/heat,dims/heat,jasondunsmore/heat,dragorosson/heat,gonzolino/heat,dragorosson/heat,maestro-hybrid-cloud/heat,takeshineshiro/heat,cwolferh/heat-scratch,openstack/heat,jasondunsmore/heat,steveb/heat,rdo-management/heat,miguelgrinberg/heat,srznew/heat,pratikmallya/heat,srznew/heat,cwolferh/heat-scratch,rdo-management/heat,redhat-openstack/heat,dims/heat,miguelgrinberg/heat,maestro-hybrid-cloud/heat,rh-s/heat,pshchelo/heat,gonzolino/heat,cryptickp/heat