ceph-validate: add key format validation
ceph-validate: add key format validation

If the user provides manually the key value for a specific keyring then
there's not valation on the content which could lead to unexpected
failures in the ceph_key module.

Closes: #5104

Signed-off-by: Dimitri Savineau <a50a620e679eed14f4e99998b821cea8884cf228@redhat.com>

ceph/ceph-ansible,ceph/ceph-ansible