Adapt for cinder multi-backend support

This depends on https://github.com/crowbar/barclamp-cinder/pull/197
This flag is used only at  line 210 to avoid do repeat the search and then later at line 214 to mean that we found a chef server. If my understanding is correct I'd suggest renaming it "chef_server_found" or something like that, to make more clear that we are not disabling ceph because of some condition is met.  At first sight looking at line 203 and 204 I assumed that there were a relationship between the nova role nova-multi-compute-kvm and disabling ceph.