choose starting concurrency based on number of local disks

[harshavardhana]

Description

choose starting concurrency based on the number of local disks

Motivation and Context

smaller setups may have fewer drives per server choosing
the concurrency based on the number of local drives, and let
the MinIO server changes the overall concurrency as
necessary.

How to test this PR?

Have a smaller setup and observe the overall concurrency chosen by the server.

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

[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