avoid 'panic' on mc admin update for single drive setup

[harshavardhana]

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contributions to the project maintainers under the Apache 2 license.

Description

avoid 'panic' on mc admin update for single drive setup

Motivation and Context

do not need to make remote networking calls for peers
on single-drive setups.

How to test this PR?

mc admin update with the single setup after the recent change

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