adding error message in case graph retrieval is throwing an error

When there is an error during retrieval of the graph, an error is raised (in `cycle_found?` method).
The error message is not stored and at the end the spec fail with the following error message:
"expected that the catalogue would include " (which is not really helpful as `@failed_resource` string is empty).

I added the catch of the error message in rescue of cycle_found? and the messag is used in `failure_message_for_should` to be more precise.