virsh: Add image set upload status file
virsh: Add image set upload status file

Given the quantity of data in an image set, the uploads take a
long time. There may also be multiple hypervisors building the
same image set and may therefore try to upload at the same time,
overwriting each other.

In order to facilitate status tracking externally (by Jenkins)
we need to provide a facility to inform the status of the image
set upload.

This patch implements a simple status file with two states in
it:

1. upload-start
2. upload-complete

Timestamps are included to allow for a janitor process to find
uploads that started and never completed. This will make it
easier to clean them up asynchronously.

JIRA: OSP-12994

Change-Id: I32e8b6fa0c046895d5be6c4b0a75950e074d752e

redhat-openstack/infrared,redhat-openstack/infrared,redhat-openstack/infrared