osd: do not make journal equal to disk when it is left off
osd: do not make journal equal to disk when it is left off

Let ceph-disk-prepare handle the default journal logic.  Putting it in
here obscures information, and makes it confusing when you specify a
dir like so:

 ceph-deploy osd foo:/srv/mydir

would turn into

 ceph-disk-prepare /srv/mydir /srv/mydir

which is nonsense.

Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@inktank.com>

rtulke/ceph-deploy,jumpstarter-io/ceph-deploy,dachary/ceph-deploy,zhouyuan/ceph-deploy,zhouyuan/ceph-deploy,shenhequnying/ceph-deploy,ceph/ceph-deploy,branto1/ceph-deploy,ktdreyer/ceph-deploy,codenrhoden/ceph-deploy,alfredodeza/ceph-deploy,ddiss/ceph-deploy,codenrhoden/ceph-deploy,ddiss/ceph-deploy,SUSE/ceph-deploy-to-be-deleted,trhoden/ceph-deploy,shenhequnying/ceph-deploy,isyippee/ceph-deploy,jumpstarter-io/ceph-deploy,Vicente-Cheng/ceph-deploy,isyippee/ceph-deploy,osynge/ceph-deploy,SUSE/ceph-deploy,ghxandsky/ceph-deploy,imzhulei/ceph-deploy,alfredodeza/ceph-deploy,ghxandsky/ceph-deploy,SUSE/ceph-deploy,SUSE/ceph-deploy-to-be-deleted,osynge/ceph-deploy,ceph/ceph-deploy,branto1/ceph-deploy,imzhulei/ceph-deploy,ktdreyer/ceph-deploy,rtulke/ceph-deploy,Vicente-Cheng/ceph-deploy,trhoden/ceph-deploy,dachary/ceph-deploy