Allow using Environment creds on AWS

[GnatorX]

What I have added/changed is:

I added the ability for the agent to pick up cred from the env. Rather than forcing users to use IAM user (by asking for access key and secret key), this allows users to user to use IAM roles. When running the agent on AWS, ideally you won't use IAM user because within AWS you have access to IAM roles. IAM roles have session timeout where IAM users do not which would prevent abuse of access if someone gain access to your creds.

The goal of my change is:

Allow a safer way to run the agent on AWS by allowing user to use IAM role rather than IAM user.

What I have tested about my change is:

Tested, working on EC2.