NSFS | NC | Allow unset 'new_buckets_path'

[shirady]

Environment info

• NooBaa Version: master
• Platform: NC

Actual behavior

1. Currently we don't have the option to unset the property new_buckets_path after the account was created.

Expected behavior

1. To allow users to unset the property new_buckets_path after the account was created when using Manage NSFS CLI.

Steps to reproduce

1. none

More information - Screenshots / Logs / Other output

Like we have the option to unset fs_backend and s3_policy.