Go1.17.2 upgrade

[sharanyad]

Summary

This upgrades Go version for building ECS agent (both Linux and Windows) to 1.17.2 (latest).

Implementation details

1. Ran goimports (// +build to //go:build) to fix static check failures
2. Ran gogenerate (os "os" to fs "io/fs") to fix static check failures
3. Use GO111MODULE=auto wherever necessary since go mod is the default in the latest versions
4. Today, customers can set HTTP_PROXY and HTTPS_PROXY proxy configurations in the /etc/ecs/ecs.config file. Latest Go includes a security fix to the net/http package, and one of the changes is the ProxyFromEnvironment function no longer returns the setting of the HTTP_PROXY environment variable for https when HTTPS_PROXY is unset.
   To update the internal proxy config after Agent has been initialized, having the http client to check for proxy environment variables for every request is necessary. Used from fenxiong@f231f86
   TestSquidProxy was failing due to the backward breaking change, this set of changes fixes it

Testing

New tests cover the changes: yes

Description for the changelog

N/A

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[angelcar]

I think the only outstanding thing is the // +build linux tag, but lgtm otherwise

[fenxiong]

🚀