support aws named profile `[profile name]` style.

Hi,

The `--profile` option should be work like aws cli. 

For example, here is sample config from [Setting and Using Named Profiles  | AWS Command Line Interface
User Guide](http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html#cli-multiple-profiles)

```
[default]
aws_access_key_id=AKIAIOSFODNN7EXAMPLE
aws_secret_access_key=wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY
region=us-east-1

[profile test-user]
aws_access_key_id=AKIAI44QH8DHBEXAMPLE
aws_secret_access_key=je7MtGbClwBF/2Zp9Utk/h3yCo8nvbEXAMPLEKEY
region=us-west-2
```
In this case, the kumogata have to be give option as `--profile 'profile test-user'` to pass profile name.
I would like to pass profile name with option `--profile test-user`.