Remove mon_initial_members option

The mon_initial_members is not used since we declare the mon section in
the ceph.conf file. Later, we could reduce the ceph.conf file by only
using the mon_host flag instead of all the mon sections.

Signed-off-by: Sébastien Han <sebastien.han@enovance.com>
Merge pull request #46 from leseb/fix-mon-initial-members

Remove mon_initial_members option