Add a way to view teraform debug logs

[Veetaha]

Terraform has a lot of useful debug logs, including logging the AWS API requests it makes.
With the usual terraform CLI it is possible to set TF_LOG env variable to get verbose debug logs info.

I propose awsrm to mimic terraform in this way and use TF_LOG env variable for viewing terraform and AWS SDK logs, or use some other kind of switch if it makes sense.

As of now having TF_LOG env var set doesn't influence awsrm behavior.
It only exposes --debug CLI flag which provides pretty terse logs of awsrm wrapper itself, which is not enough