Optimse the external ceph configure action

1. refer to the docs of external ceph for manila[0],
the ceph.conf will be found in ``/etc/kolla/config/manila/``,
so remove the unnecessary ``manila/manila-share`` folder
2. remove the ``manila/manila/ceph.client.manila.keyring``

[0]: https://github.com/openstack/kolla-ansible/blob/master/doc/source/reference/external-ceph-guide.rst

Change-Id: I93308b859b769a856c0519347277f01947f86f3d