Internal Server Error trying to create workspaces from a mashup with garbage in behaviours descriptions

[aarranz]

WireCloud is failing with an internal server error when trying use a mashup template with garbage in the description of the behaviours. Such a mashup template can be obtained due to bug #248 so, for now, we will have to support using those corrupted mashups templates without raising a 422 error code (Evidently, a 500 error code is not the correct response).

In a future, WireCloud will disallow mashups with garbage.