Description of problem:
When attempting to install a RHEL-5 guest on F-8 Test3 (plus latest updates),
using this command-line:

# virt-install -d -n manage -r 512 -f /var/lib/xen/images/manage.dsk -s 10
--nonsparse -p --nographics -l
nfs:bigpapi:/vol/engineering/redhat/rhel5-server-x86_64

I get the following backtrace:

Tue, 09 Oct 2007 09:40:32 DEBUG    Disk path not found: Assuming file disk type.


Starting install...
libvir: Xen Daemon error : GET operation failed: 
Tue, 09 Oct 2007 09:40:32 DEBUG    Preparing mount at
/var/lib/xen/virtinstmnt.ivNS7C
Tue, 09 Oct 2007 09:40:32 DEBUG    Distro None.
Tue, 09 Oct 2007 09:40:32 DEBUG    Acquiring file from
/var/lib/xen/virtinstmnt.ivNS7C/fedora.css
Tue, 09 Oct 2007 09:40:32 DEBUG    Cleaning up mount at
/var/lib/xen/virtinstmnt.ivNS7C
Invalid file location given: No such file or directory
Domain installation may not have been
 successful.  If it was, you can restart your domain
 by running 'virsh start manage'; otherwise, please
 restart your installation.
Tue, 09 Oct 2007 09:40:32 ERROR    Invalid file location given: No such file or
directory
Traceback (most recent call last):
  File "/usr/sbin/virt-install", line 485, in <module>
    main()
  File "/usr/sbin/virt-install", line 449, in main
    dom = guest.start_install(conscb,progresscb)
  File "/usr/lib/python2.5/site-packages/virtinst/Guest.py", line 722, in
start_install
    self._prepare_install(meter)
  File "/usr/lib/python2.5/site-packages/virtinst/ParaVirtGuest.py", line 48, in
_prepare_install
    self._installer.prepare(guest = self, meter = meter)
  File "/usr/lib/python2.5/site-packages/virtinst/DistroManager.py", line 683,
in prepare
    self._prepare_kernel_and_initrd(guest, distro, meter)
  File "/usr/lib/python2.5/site-packages/virtinst/DistroManager.py", line 653,
in _prepare_kernel_and_initrd
    distro = distro)
  File "/usr/lib/python2.5/site-packages/virtinst/DistroManager.py", line 583,
in acquireKernel
    progresscb=progresscb, distro=distro, scratchdir=scratchdir)
  File "/usr/lib/python2.5/site-packages/virtinst/DistroManager.py", line 566,
in _storeForDistro
    if store.isValidStore(fetcher, progresscb):
  File "/usr/lib/python2.5/site-packages/virtinst/DistroManager.py", line 213,
in isValidStore
    if fetcher.hasFile("fedora.css", progresscb):
  File "/usr/lib/python2.5/site-packages/virtinst/DistroManager.py", line 160,
in hasFile
    tmpfile = self.acquireFile(filename, progresscb)
  File "/usr/lib/python2.5/site-packages/virtinst/DistroManager.py", line 150,
in acquireFile
    raise ValueError, _("Invalid file location given: ") + msg
ValueError: Invalid file location given: No such file or directory

The problem is in virtinst/DistroManager.py; if you can't find fedora.css in the
FedoraImageStore.isValidStore() method, it stacktraces instead of trying
additional OS's.  That is, *any* PV guest that is not Fedora is going to fail,
since it will stack trace when looking in the directory structure.  In
_storeForDistro, I changed:

    for store in stores:
        if store.isValidStore(fetcher, progresscb):
            return store

to:

    for store in stores:
        try:
            if store.isValidStore(fetcher, progresscb):
                return store
        except:
            continue

which allowed me to start the RHEL-5 install.  This is with
python-virtinst-0.300.1-2.fc8, by the way.