Fix crash on nova-compute-kvm nodes when they don't also host ceph

We simply don't have the fsid attribute in our own attributes, so we
need to look for that.

https://bugzilla.novell.com/show_bug.cgi?id=885439
Merge pull request #83 from vuntz/fix-nova-ceph

Fix crash on nova-compute-kvm nodes when they don't also host ceph