Code review comment for lp://staging/~jelmer/loggerhead/docker-improvements

The py35 tests fail:

14:20:21 O: Traceback (most recent call last):
14:20:21 O: File "<string>", line 1, in <module>
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/setup.py", line 771, in <module>
14:20:21 O: setup(**ARGS)
14:20:21 O: File "/usr/lib/python3.5/distutils/core.py", line 148, in setup
14:20:21 O: dist.run_commands()
14:20:21 O: File "/usr/lib/python3.5/distutils/dist.py", line 955, in run_commands
14:20:21 O: self.run_command(cmd)
14:20:21 O: File "/usr/lib/python3.5/distutils/dist.py", line 974, in run_command
14:20:21 O: cmd_obj.run()
14:20:21 O: File "/workspace/loggerhead/loggerhead/work/.tox/py35/lib/python3.5/site-packages/setuptools/command/install.py", line 61, in run
14:20:21 O: return orig.install.run(self)
14:20:21 O: File "/usr/lib/python3.5/distutils/command/install.py", line 583, in run
14:20:21 O: self.run_command('build')
14:20:21 O: File "/usr/lib/python3.5/distutils/cmd.py", line 313, in run_command
14:20:21 O: self.distribution.run_command(command)
14:20:21 O: File "/usr/lib/python3.5/distutils/dist.py", line 974, in run_command
14:20:21 O: cmd_obj.run()
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/setup.py", line 182, in run
14:20:21 O: generate_docs.main(argv=["brz", "man"])
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/tools/generate_docs.py", line 96, in main
14:20:21 O: infogen_mod.infogen(options, outfile)
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/breezy/doc_generate/autodoc_man.py", line 54, in infogen
14:20:21 O: outfile.write(man_escape(getcommand_list(params)))
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/breezy/doc_generate/autodoc_man.py", line 85, in getcommand_list
14:20:21 O: for cmd_name in command_name_list():
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/breezy/doc_generate/autodoc_man.py", line 71, in command_name_list
14:20:21 O: command_names = breezy.commands.builtin_command_names()
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/breezy/commands.py", line 234, in builtin_command_names
14:20:21 O: _register_builtin_commands()
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/breezy/commands.py", line 192, in _register_builtin_commands
14:20:21 O: import breezy.builtins
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/breezy/builtins.py", line 24, in <module>
14:20:21 O: import breezy.git
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/breezy/git/__init__.py", line 313, in <module>
14:20:21 O: from ..branch import (
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/breezy/branch.py", line 38, in <module>
14:20:21 O: from . import (
14:20:21 O: File "/tmp/pip-build-i7t0_1g5/breezy/breezy/revision.py", line 52
14:20:21 O: parent_ids: List[RevisionID]
14:20:21 O: ^
14:20:21 O: SyntaxError: invalid syntax