Code review comment for lp:~chris.macnaughton/mojo/py3002

Not quite py3 ready:

2018-01-24 11:10:49 [INFO] Rsyncing /home/ubuntu/mojo-openstack-specs to /srv/mojo/openstack/xenial/_20181024_111047/spec
2018-01-24 11:10:50 [INFO] Retrieve the spec's manifest
2018-01-24 11:10:50 [INFO] Manifest comment:

#############################################################################
Collect the charm branches from Launchpad
#############################################################################

2018-01-24 11:10:50 [INFO] Building resource tree
2018-01-24 11:10:50 [ERROR] Unknown error
Traceback (most recent call last):
  File "/home/ubuntu/charm-test-infra/.tox/clients/lib/python3.5/site-packages/mojo/cli.py", line 628, in run_with_args
    args.func(args)
  File "/home/ubuntu/charm-test-infra/.tox/clients/lib/python3.5/site-packages/mojo/utils.py", line 305, in wrapped
    return method(*args, **kwargs)
  File "/home/ubuntu/charm-test-infra/.tox/clients/lib/python3.5/site-packages/mojo/cli.py", line 346, in run_from_manifest
    manifest.run(project, workspace, args.stage)
  File "/home/ubuntu/charm-test-infra/.tox/clients/lib/python3.5/site-packages/mojo/manifest.py", line 100, in run
    auto_repo=auto_repo)
  File "/home/ubuntu/charm-test-infra/.tox/clients/lib/python3.5/site-packages/mojo/phase.py", line 221, in run
    rendered_collect.write(Template(inp.read()).render(**tmpl_vars))
  File "/home/ubuntu/charm-test-infra/.tox/clients/lib/python3.5/tempfile.py", line 622, in func_wrapper
    return func(*args, **kwargs)
TypeError: a bytes-like object is required, not 'str'