ceph.conf is loaded by qemu, not libvirt.
Since qemu runs as the nova user, ceph.conf owned by root
causes a permission error. The logs in
/var/log/libvirt/qemu/instance-*.log reveal the error.

This change fixes the issue by changing the ownership of ceph.conf
in nova-libvirt to the nova user.

Closes-Bug: #1861513
Change-Id: I1881f51a6c8508f0f186a5623443343dc1df41d4
Signed-off-by: Ning Yao <yaoning@unitedstack.com>