ceph-disk-activate: don't override default or configured osd journal path

There is no reason not to rely on the default or obey any configured
value here.

Fixes: #4031
Signed-off-by: Sage Weil <sage@inktank.com>
ceph-disk-activate: rely on default/configured keyring path

No reason to override the default or configured value here.

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