maas-test fails if saucy image is not perfectly up to date

maas-test fails if the saucy image cannot install language packs, and that happened to me today because for some reason the package files were out of date. The following line fixed the problem:

  # Install the English language pack first. If this is not done
  # before postgres is installed, on some systems it won't be able to
  # set up its main cluster.
  # TODO: Is there no better way to ensure this, e.g. through a
  # dependency?
+ self.kvm_fixture.run_command(['sudo', 'apt-get', 'update'], check_call=True)
  self.kvm_fixture.install_packages(['language-pack-en'])

I suspect the fix can be made more robust, with a useful logged error message if the update fails, but this was sufficient to get me past this particular hurdle on the day :)