Add debug log for device detach libvirt error
Add debug log for device detach libvirt error

We see a new way of virDomainDetachDeviceFlags() to fail in bug 1931716.
This patch logs the libvirt error code and error message.

Change-Id: I7ec4ea68a933d1cb415c4adee97a508cf9611468
Related-Bug: #1931716

mahak/nova,mahak/nova,openstack/nova,mahak/nova,openstack/nova,openstack/nova