Fix a possible service freeze after perf object

[vadmeste]

Description

The S3 service can be frozen indefinitely if a client or mc asks for object
perf API but quits early or has some networking issues. The reason is
that partialWrite() can block indefinitely.

This commit makes partialWrite() listens to context cancellation as well. It
also renames deadlinedCtx to healthCtx since it covers handler context
cancellation and not only not only the speedtest deadline.

Motivation and Context

Fix occasional freeze in Play.

How to test this PR?

Hard to test

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