allow single drive mode to run on root disk

[harshavardhana]

Description

allow single drive mode to run on root disk

Motivation and Context

for practical reasons allow, single drive setups
to run on root disks without any special settings.

How to test this PR?

Nothing just run the latest release on / it shall fail
with some complaints about root disk.

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)
• Documentation updated
• Unit tests added/updated

[vadmeste]

LGTM

[minio-trusted]

Mint Automation

Test	Result
mint-large-bucket.sh	✔️
mint-fs.sh	✔️
mint-gateway-s3.sh	✔️
mint-erasure.sh	✔️
mint-dist-erasure.sh	✔️
mint-compress-encrypt-dist-erasure.sh	✔️
mint-pools.sh	✔️
Deleting image on docker hub
Deleting image locally