setup_vm requires the working dir to contain vms.conf

[Vincent Ladeuil]

When using setup_vm.py outside of the setup_vm directory when running from sources, I end up with:

$ setup_vm.py --install --download precise-server-pristine
Traceback (most recent call last):
  File "/home/vila/bin/setup_vm.py", line 1203, in <module>
    run()
  File "/home/vila/bin/setup_vm.py", line 1195, in run
    cmd.run()
  File "/home/vila/bin/setup_vm.py", line 1146, in run
    self.vm.download_cloud_image(force=True)
  File "/home/vila/bin/setup_vm.py", line 891, in download_cloud_image
    return self._download_in_cache(self.conf.get('vm.cloud_image_url'),
  File "/usr/lib/python2.7/dist-packages/bzrlib/config.py", line 3739, in get
    value = expand_and_convert(value)
  File "/usr/lib/python2.7/dist-packages/bzrlib/config.py", line 3713, in expand_and_convert
    val = self._expand_options_in_string(val)
  File "/usr/lib/python2.7/dist-packages/bzrlib/config.py", line 3793, in _expand_options_in_string
    raise errors.ExpandingUnknownOption(name, string)
bzrlib.errors.ExpandingUnknownOption: Option vm.release is not defined while expanding "http://cloud-images.ubuntu.com/{vm.release}/current/".

It would be better if setup_vm could find setup_vm/vms.conf without relying on the current directory.