allow catalogs to be embedded into workflow when workflow contains sub workflows

Ian Harry (PyCBC and LIGO) proposed that it would be great to have this supported. Currently we do not allow the SiteCatalog and TransformationCatalog to be embedded into a workflow when the workflow contains SubWorkflow jobs: https://github.com/pegasus-isi/pegasus/blob/4293107fb71ca595fafca5df7c39812b14c29e26/packages/pegasus-api/src/Pegasus/api/workflow.py#L1394-L1405

When commenting out this block of code, Ian noted that the hierarchical workflow appeared to run correctly, however we need to further investigate to see if that will true in all case.

notes: https://docs.google.com/document/d/1e6rfkJDiXN3eKhSma7V_PmihfsgcaK9hisfOtPK6KrY/edit