Bump terraform-svchost to 0.2.1

[brandonc]

When connected to HCPTF/TFE, terraform-svchost performs some service discovery request, at least two during terraform init. Troublingly, terraform-svchost only attempts one request for each discovery, so any network or service failure can cause CLI errors before plan or apply begins. We've noticed that the vast majoring of these requests succeed in < 100ms, but at scale, many requests per day can hang for various reasons, including temporary internet connection problems or just basic service availability during transition states.

terraform-svchost v0.2.1 adds retryablehttp, attempting the discovery request up to 4 times (3 retries) with a 5 second timeout.

In practical terms, service discovery will time out after 20 seconds if there is no header response from 4 requests, whereas previously it would time out after 11 seconds if there was no header response from 1 request.

Target Release

1.15.0

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.