external ceph does not copy per-node ceph keyring

When deploying nova with an advanced configuration with external ceph and per host nova configurations files, the "Check nova keyring file" fails because it only checks the existence of top level "{{ node_custom_config }}/nova/{{ ceph_nova_keyring }}". It needs to also check: "{{ node_custom_config }}/nova/{{ inventory_hostname }}/{{ ceph_nova_keyring }}".

Use case, certain nodes that are destined for host aggregate groups need to be able to connect to different ceph clusters/configurations.

**Bug Report**

What happened:
TASK [nova-cell : Check nova keyring file] ********************************************************************************************************************************************
fatal: [<ip/hostname> -> localhost]: FAILED! => {"changed": false, "failed_when_result": true, "stat": {"exists": false}}

What you expected to happen:
This check should have passed as all hosts provide the ceph.client.nova.keyring file in their host specific folder under {{ node_custom_config}}/nova/{{ inventory_hostname }}

How to reproduce it (minimal and precise):
Utilize only {{ node_custom_config}}/nova/{{ inventory_hostname }} to provide kolla-ansible with ceph.client.nova.keyring

**Environment**:
* OS (e.g. from /etc/os-release): VERSION="18.04.4 LTS (Bionic Beaver)"
* Kernel (e.g. `uname -a`): Linux 4.15.0-101-generic #102-Ubuntu SMP Mon May 11 10:07:26 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
* Docker version if applicable (e.g. `docker version`): 19.03.11
* Kolla-Ansible version (e.g. `git head or tag or stable branch` or pip package version if using release): stable/train but this affects master as well
* Docker image Install type (source/binary): binary
* Docker image distribution: ubuntu
* Are you using official images from Docker Hub or self built? Docker Hub
* If self built - Kolla version and environment used to build:
* Share your inventory file, globals.yml and other configuration files if relevant