Unable to create/open notebook when disk is full. Misleading error.

Asked to duplicate here from jupyterlab/jupyterlab#6248.

When running out of disk space Jupyter Lab starts giving error messages which seem unrelated.

When checking the logs you can see disk space related errors

[I 2019-04-25 15:40:51.771 SingleUserLabApp handlers:153] Creating new notebook in /work/revolver
[E 2019-04-25 15:40:51.772 SingleUserLabApp filemanager:485] Error while saving file: work/revolver/Untitled.ipynb database or disk is full
    Traceback (most recent call last):
      File "/opt/conda/lib/python3.6/site-packages/notebook/services/contents/filemanager.py", line 470, in save
        self.check_and_sign(nb, path)
      File "/opt/conda/lib/python3.6/site-packages/notebook/services/contents/manager.py", line 487, in check_and_sign
        self.notary.sign(nb)
      File "/opt/conda/lib/python3.6/site-packages/nbformat/sign.py", line 449, in sign
        self.store.store_signature(signature, self.algorithm)
      File "/opt/conda/lib/python3.6/site-packages/nbformat/sign.py", line 207, in store_signature
        if not self.check_signature(digest, algorithm):
      File "/opt/conda/lib/python3.6/site-packages/nbformat/sign.py", line 239, in check_signature
        (datetime.utcnow(), algorithm, digest),
    sqlite3.OperationalError: database or disk is full

Steps to reproduce:

• Run Jupyter Lab on a machine with a size limited disk
• Fill the disk (dd if=/dev/zero of=/path/to/some/file until full)
• Try to create or open a notebook

Reproduce the issue by filling a size-limited disk, then trace notebook creation and saving through handlers, notebook/services/contents/filemanager.py, manager.py, and nbformat/sign.py. Check how the sqlite3.OperationalError is surfaced during create or open, and use the reported disk-full scenario as the completion check: the user should receive an appropriate disk-space error instead of an unrelated message.