Refactoring to make backend configuration accessible from outside Client. refs #1971

Signed-off-by: Daira Hopwood <david-sarah@jacaranda.org>
Refactoring to make node config accessible without actually creating a Node. refs #1971

Signed-off-by: Daira Hopwood <david-sarah@jacaranda.org>
A missing tahoe.cfg should be an error. refs #1971

Signed-off-by: Daira Hopwood <david-sarah@jacaranda.org>
Add 'tahoe admin create-container' command. refs #1971

Signed-off-by: Daira Hopwood <david-sarah@jacaranda.org>
Fix incorrect calls to create and delete S3 buckets in S3Container. refs #1971

Signed-off-by: Daira Hopwood <david-sarah@jacaranda.org>