Added protection for non existent VNFs, referenced in the service descriptor.
Added protection for non existent VNFs, referenced in the service descriptor.

dang03/son-cli,dang03/son-cli,sonata-nfv/son-cli,stevenvanrossem/son-cli,stevenvanrossem/son-cli,lconceicao/son-cli,stevenvanrossem/son-cli,edmaas/son-cli,edmaas/son-cli,dang03/son-cli,edmaas/son-cli,sonata-nfv/son-cli,stevenvanrossem/son-cli,stevenvanrossem/son-cli,lconceicao/son-cli,lconceicao/son-cli,sonata-nfv/son-cli,dang03/son-cli,edmaas/son-cli,edmaas/son-cli,dang03/son-cli,sonata-nfv/son-cli,lconceicao/son-cli,sonata-nfv/son-cli,lconceicao/son-cli