I'm not seeing anything suspicious for recent nova commits in the compute manager or libvirt driver around snapshots or creating/rotating backups, so my guess is this is just a racy test and the timeout is going to be hit sometimes if the backing host is slow to snapshot the image.
I'm not seeing anything suspicious for recent nova commits in the compute manager or libvirt driver around snapshots or creating/rotating backups, so my guess is this is just a racy test and the timeout is going to be hit sometimes if the backing host is slow to snapshot the image.