Feature request: make logger configurable

[fujiwara]

Hi.

I'd like to use terraform-svchost in my project tfstate-lookup for TFE service discovery.

Currently, terraform-svchost uses log.Printf for debug logging, but the output cannot be redirected or suppressed by the consuming application. As a result, users of tfstate-lookup would be forced to see [DEBUG] messages on stderr.

Since tfstate-lookup is used as a library in other products, this behavior is problematic.
Would you consider making the logger configurable, so that consumers can customize or suppress the log output?