[SPARK-10532][EC2] Added --profile option to specify the name of profile

"profiles" give us the way that you can specify the set of credentials you want to use when you initialize a connection to AWS.

You can keep multiple sets of credentials in the same credentials files using different profile names.
For example, you can use --profile option to do that when you use "aws cli tool".

http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html

Author: teramonagi <teramonagi@gmail.com>

Closes #8696 from teramonagi/SPARK-10532.