test isolation error in remote tests

 affects bzr
 status confirmed
 importance high
 done

This is likely affecting test accuracy

^^^^[log from
bzrlib.tests.branch_implementations.test_stacking.TestStacking.test_autopack_when_stacked(RemoteBranchFormat-default)]
----------------------------------------------------------------------
Traceback (most recent call last):
  File
"/home/robertc/source/baz/pending/autopack-cross-format-fetch/bzrlib/tests/branch_implementations/test_stacking.py", line 314, in test_autopack_when_stacked
    if not self.branch_format.supports_stacking():
  File
"/home/robertc/source/baz/pending/autopack-cross-format-fetch/bzrlib/remote.py", line 1929, in supports_stacking
    self._ensure_real()
  File
"/home/robertc/source/baz/pending/autopack-cross-format-fetch/bzrlib/remote.py", line 1845, in _ensure_real
    self._network_name)
  File
"/home/robertc/source/baz/pending/autopack-cross-format-fetch/bzrlib/registry.py", line 260, in get
    r = Registry.get(self, format_string)
  File
"/home/robertc/source/baz/pending/autopack-cross-format-fetch/bzrlib/registry.py", line 173, in get
    return self._dict[self._get_key_or_default(key)].get_obj()
  File
"/home/robertc/source/baz/pending/autopack-cross-format-fetch/bzrlib/registry.py", line 191, in _get_key_or_default
    raise KeyError('Key is None, and no default key is set')
KeyError: 'Key is None, and no default key is set'

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