Reduce collisions with aws-cli

[igolan]

Frost overrides ~/.aws/config which is also used by aws-cli.
On override, Frost doesn't create a [default] profile which is used by aws-cli (unless AWS_PROFILE env variable is set), so if a user uses Frost and don't set AWS_PROFILE, aws-cli won't work properly with Frost.

A possible solution is to keep the [default] profile in ~/.aws/config (if exists) on override.