add-osd.yml: Add become flag for ceph-validate

add-osd.yml: Add become flag for ceph-validate

The check_devices task fails if the ceph-validate role isn't executed
as a privileged user (Permission denied).

failed: [osd0] (item=/dev/sdb) => {"changed": false, "err": "Error:
Error opening /dev/sdb: Permission denied\n", "item": "/dev/sdb",
"msg": "Error while getting device information with parted script:
'/sbin/parted -s -m /dev/sdb -- unit 'MiB' print'", "out": "", "rc": 1}

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>