New port: security/aws-vault

AWS Vault is a tool to securely store and access AWS credentials in a
development environment.

AWS Vault stores IAM credentials in your operating system's secure keystore and
then generates temporary credentials from those to expose to your shell and
applications. It's designed to be complementary to the AWS CLI tools, and is
aware of your profiles and configuration in ~/.aws/config.

WWW: https://github.com/99designs/aws-vault

Approved by: araujo (mentor)
Differential Revision: https://reviews.freebsd.org/D21955