HyperCli need support regions

[Tim-Zhang]

As our new region EU-region is about to go online, the CLI need support region specified.
According to http://docs.aws.amazon.com/zh_cn/cli/latest/userguide/cli-chap-getting-started.html

we have to do the following 3 jobs

1. Implement region field in config file
2. Implement --region in command line
3. Implement HYPER_DEFAULT_REGION env(I think the env is not so important, so whether to implement this is up to developers)

The precedence

--region > HYPER_DEFAULT_REGION > region config