Fixes previous pull request #8978
An oversight meant that unrestricted API keys
never called b2_list_buckets,
meaning the root remote could not be listed.
The call is now made in the event there are no allowed buckets,
indicating an unrestricted API key
Fixes#9007
Backblaze has updated its b2_authorize_account API endpoint, newly created
application keys are now "multi-bucket" keys, capable of being limited to
multiple buckets. These keys can only be used with the v4 endpoint, not v1 which
returns an HTTP 400.
This commit switches authorization to the v4 endpoint, and allowing such keys to
work with any of the allowed buckets.
With multi-bucket keys, missing restricted buckets can be non-fatal.
Supports listing root with multi-bucket API keys
DianaNites