Added a state function to automate EC2 authentication
Added a state function to automate EC2 authentication

Wrote a state function that will:
1. Verify that the target EC2 role exists
2. Retrieve the PKCS7 key from instance metadata
3. Authenticate against the Vault server using `auth_ec2`
4. Write the resulting client token and nonce to the minion config
5. Load the new config data in the running minion
6. Return the response data

mitodl/salt-extensions