info: Correctly show pool config with offline node(s)

[vadmeste]

Description

There is a silly bug when the number of disks per set is showing
incorrectly when the last node of a pool is offline.

Fix the code by using the new drives per set/sets count information
sent directly by the server.

Motivation and Context

Fix wrong report of disks per set in mc admin info

How to test this PR?

• Run a cluster of 4 nodes and kill the last server
• Run mc admin info and check for disks per set field

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Optimization (provides speedup with no functional changes)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• Fixes a regression (If yes, please add commit-id or PR # here)
• Unit tests added/updated
• Internal documentation updated
• Create a documentation update request here