Fix OSD update during startup

Proviously we used osd_crush_update_on_start: true, this was interpreted
by Ansible as a boolean and appeared as 'True' inside the Ceph configuration
file. However the Ceph's init script is looking for 'true'.

Signed-off-by: Sébastien Han <sebastien.han@enovance.com>
Merge pull request #114 from leseb/fix-osd-option

Fix OSD update during startup