Documentation changes about Ceph datastore CEPH_USER attr
* Change: CEPH_USER is not mandatory into CEPH datastore conf to become backwards comp.
Doc Fix: one.datastore.allocate IN string cluster ID is mandatory
Fix: one.datastore.allocate add IN cluster ID is mandatory
Fix: one.datastore.allocate add IN cluster ID is mandatory
Merge pull request #12 from alvarosimon/master

Documentation changes about Ceph datastore CEPH_USER attr