When a user calls the volume-update API, we swap_volume in the libvirt
driver from the old volume attachment to the new volume attachment.
Currently, we're saving the domain XML with the old configuration prior
to updating the volume and upon a soft-reboot request, it results in an
error:
Instance soft reboot failed: Cannot access storage file <old path>
and falls back to a hard reboot, which is like pulling the power cord,
possibly resulting in file system inconsistencies.
This changes to saving the new, updated domain XML after the volume
swap.
Closes-Bug: #1713857
Change-Id: I166cde5ad8b00699e4ec02609f0d7b69236d855d
5b008c6540