osd: OSDMap: fix output from ceph status --format=json for num_in_osds

num_up_osds returns as an int value, while num_in_osds returns as a string.
Since only an int can be returned from get_num_in_osds(), num_in_osds should
should also be an int to remain consistant with num_up_osds.

Fixes: 7159

Signed-off-by: Tyler Brekke <tyler.brekke@inktank.com>