Print tgenv [INFO] messages into stderr

[eorea]

Print tgenv [INFO] messages into stderr since it messes up the output from state pull command, this also affects the output command.

[terragrunt] 2020/06/11 10:28:53 Running command: terraform state pull
\e[0;32m[INFO] Getting version from tgenv-version-name\e[0;39m
\e[0;32m[INFO] TGENV_VERSION is 0.23.24\e[0;39m
{
... tfstate content
}

[terragrunt] 2020/06/11 10:32:37 Running command: terraform output -json
\e[0;32m[INFO] Getting version from tgenv-version-name\e[0;39m
\e[0;32m[INFO] TGENV_VERSION is 0.23.24\e[0;39m
{
... terraform outputs
}

[spider-network]

Please release this, because it generates so many issues when you deal with state moves and so one.

[yusukegoto]

@cunymatthieu
Hello, thanks for sharing tgenv.
Is there any blocker to merge this PR?