keyerror: format

Perhaps as fallout from bug 277398 (if that's in fact already fixed), running "bzr usertest ../testdata/mysql*tar.gz" currently fails with a failure to expand a 'format' option in one of the scripts. I haven't investigated yet how it's supposed to be getting set.

=== Task BranchTask (bzrlib.plugins.usertest.scripts.script_common) ===
bzr: ERROR: exceptions.KeyError: 'format'

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 926, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 1126, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 691, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 713, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 135, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 165, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/home/bench/.bazaar/plugins/usertest/__init__.py", line 354, in run
    strict=strict, url=url)
  File "/home/bench/.bazaar/plugins/usertest/suiterunner.py", line 300, in run_suite
    all_dynamic_params, verbose=verbose, strict=strict)
  File "/home/bench/.bazaar/plugins/usertest/suiterunner.py", line 337, in run_tests
    [tool], dynamic_params, per_tree_params, verbose, strict)[0]
  File "/home/bench/.bazaar/plugins/usertest/suiterunner.py", line 205, in _run_task_on_dirs
    prof_out_template)
  File "/home/bench/.bazaar/plugins/usertest/userscript.py", line 230, in get_script_for
    script, exceptions = self._get_raw_script_for(tool, params)
  File "/home/bench/.bazaar/plugins/usertest/userscript.py", line 187, in _get_raw_script_for
    subst_result = template.substitute(params)
  File "/usr/lib/python2.7/string.py", line 172, in substitute
    return self.pattern.sub(convert, self.template)
  File "/usr/lib/python2.7/string.py", line 162, in convert
    val = mapping[named]
KeyError: 'format'