title: terraform cli does not accept aws credentials
body: <p>I am trying to create ec2 instance using terraform. Passing credentials through terraform cli fails, while hardcoding it in main.tf works fine</p>
  
  <p>This is to create ec2 instance dynamically using terraform</p>
  
  <p>terraform apply works with following main.tf</p>
  
  <pre><code>provider "aws" {
    region     = "us-west-2"
    access_key = "hard-coded-access-key"
    secret_key = "hard-coded-secret-key"
  }
  resource "aws_instance" "ec2-instance" {
    ami = "ami-id"
    instance_type = "t2.micro"
    tags {
      Name = "test-inst"
     }
  }
  </code></pre>
  
  <p>while the following does not work:</p>
  
  <pre><code>terraform apply -var access_key="hard-coded-access-key" -var secret_key="hard-coded-secret-key"
  </code></pre>
  
  <p>Is there any difference in the above two ways of running the commands? As per terraform documentation both of the above should work.</p>