mon: do not serialized container bootstrap

mon: do not serialized container bootstrap

This commit unifies the container and non-container code, which in the
meantime gives use the ability to deploy N mon container at the same
time without having to serialized the deployment. This will drastically
reduces the time needed to bootstrap the cluster.
Note, this is only possible since Nautilus because the monitors are
bootstrap the initial keys on their own once they reach quorum. In the
Nautilus version of the ceph-container mon, we stopped generating the
keys 'manually' from inside the container, for more detail see: https://github.com/ceph/ceph-container/pull/1238

Signed-off-by: Sébastien Han <seb@redhat.com>