cephjournal mount point, file system, min size

 * remove mount point from cephjournal volume definition
 * use generator for min size instead of hardcoded 0
 * change file system from xfs to ext4 for better performance
 * change type from raid to partition for Ubuntu

Change-Id: I86c7a03fea6cc808820962a04734468680ef2b71
Merge "cephjournal mount point, file system, min size"