Support AWS in addition to VirtualBox

Steps to provision to aws/ec2 machine.

- Go to aws/IAM <https://console.aws.amazon.com/iam/home?region=us-west-1#users> console
- Create a new access key and save the KEY and SECRET
- Go to aws/region:us-east-1/ec2 keypairs page <https://console.aws.amazon.com/ec2/v2/home?region=us-east-1#KeyPairs:sort=keyName>
- Create a new pair and call it vagrant
- Save vagrant.pem file into your home

$ cat > env.sh
export AWS_KEY="<YOUR KEY>"
export AWS_SECRET="<YOUR SECRET>"
export AWS_KEYNAME="vagrant"
export AWS_KEYPATH="~/vagrant.pem"
CTRL+D

$ chmod +x env.sh
$ . ./env.sh
$ vagrant up --provider=aws