Covert API to use HeatAPIException subclasses, instead of
plain webob exceptions, which cannot be correctly serialized
by the wsgi controller, and map engine errors to API exceptions
so the raw engine exception is not propogated to the user.
ref #125
fixes #150
Change-Id: I164c71e12ed29f40ad67188b645ca7ad2fa1fee8
Signed-off-by: Steven Hardy <shardy@redhat.com>