pickup aws credentials from ~/.aws/credentials

[yarikoptic]

It would be a typical use case that users might have already ~/.aws/credentials which is a typical python config file with possibly multiple sections containing credentials. If user decides to use our aws-ec2 backend, and we detect absent in our configuration aws credentials, we should ask (if interactive session) either the user would like to use any of those credentials, and copy them over.

It also brings up the question of multiple possible credentials, which I sketched in #472

[chaselgrove]

@yarikoptic did you mean ~/.aws/config? This is the standard AWS configuration file and is picked up by the boto calls.

[yarikoptic]

Hm, might be. I will ask Google later on either anything stores in credentials - I might have indeed just mystyped.