uvt-simplestreams-libvirt crashes if /var/lib/uvtool is a symlink

On my system, I ran out of room in /var/lib, so I made /var/lib/uvtool a symlink to /home/spill/uvtool (and moved everything over).

Now, uvt-simplestreams-libvirt crashes as follows:

$ uvt-simplestreams-libvirt sync release=trusty arch=amd64 label=daily
Traceback (most recent call last):
  File "/usr/bin/uvt-simplestreams-libvirt", line 27, in <module>
    uvtool.libvirt.simplestreams.main()
  File "/usr/lib/python2.7/dist-packages/uvtool/libvirt/simplestreams.py", line 326, in main
    args.func(args)
  File "/usr/lib/python2.7/dist-packages/uvtool/libvirt/simplestreams.py", line 270, in main_sync
    clean_extraneous_images()
  File "/usr/lib/python2.7/dist-packages/uvtool/libvirt/simplestreams.py", line 152, in clean_extraneous_images
    filter_by_dir=IMAGE_DIR)
  File "/usr/lib/python2.7/dist-packages/uvtool/libvirt/__init__.py", line 222, in get_all_domain_volume_names
    volume = conn.storageVolLookupByKey(path)
  File "/usr/lib/python2.7/dist-packages/libvirt.py", line 3584, in storageVolLookupByKey
    if ret is None:raise libvirtError('virStorageVolLookupByKey() failed', conn=self)
libvirt.libvirtError: Storage volume not found: no storage vol with matching key /home/spill/uvtool/libvirt/images/x-uvt-b64-Y29tLnVidW50dS5jbG91ZDpzZXJ2ZXI6MTIuMDQ6YW1kNjQgMjAxMzEyMDU=

(I called this without the --source parameter I should have used, but this doesn't matter for the purposes of this bug).

"virsh vol-list --pool uvtool" shows me that this volume does exist, but of course it has a key of /var/lib/uvtool/..., not the symlinked location.

Importance: Medium since it this bug only manifests itself on a non-standard system configuration.