On the client side it should use only 'qubesadmin'. In practice, those
few are trivial to replace:
- get_disk_usage() is also available in shutil (as disk_usage())
- BackupCancelledError should be used from qubesadmin.exc anyway (there
was also a typo)
Remove also test-packages/qubes to let pylint detect such issues in the
future.
QubesOS/qubes-issues#5403