[7.0.x] Bump go to 1.17.5 (#871)

[bernardjkim]

Description

Bump go version to 1.17.5. Applied some changes that were required due to module changes in Go 1.16.

• go install now requires a version suffix.
• Go defaults to GO111MODULE=on. We need to set GO111MODULE=off in places we want to continue using GOPATH mode.

Linked tickets and PRs

• Ports https://github.com/gravitational/planet/pull/871
• Refs https://github.com/gravitational/gravity/issues/2693