.ipynb_checkpoints doesn't respect umask

[dclong]

I used the following configuration in /etc/jupyter/jupyter_notebook_config.py. Newly created notebooks have the right permission (664), however the .ipynb_checkpoints folders do not.

import os
os.umask(0o002)

[dclong]

And setfacl doesn't make .ipynb_checkpoints directories have the right permission, either.

[dclong]

I quickly checked the code and found the following piece of code which might be the root cause.

./services/contents/filecheckpoints.py:            ensure_dir_exists(cp_dir)

The function ensure_dir_exists is in ipython_genutils/path.py. It has a parameter mode with default value 0o755. Passing the right mode to ensure_dir_exists might resolve the issue.

[takluyver]

I suspect that someone - possibly me - saw that the default for os.makedirs() was 0o777 and assumed that that it would actually create a world-writable directory by default. So I implemented a default equivalent to umask 0o022. I think we can probably let the default be determined by the umask.

[dclong]

@takluyver
That would resolve the issue.

[takluyver]

See #2924