Remove the hardcoded default profile. The SDK will already set the de…

[sunds]

…fault profile if none is specified. This allows the end user to override the profile in /etc/ecs/ecs.config with the environment variable AWS_PROFILE

Summary

Implementation details

Testing

New tests cover the changes:

Description for the changelog

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[Realmonia]

This is to fix https://github.com/aws/amazon-ecs-agent/issues/3241

[Realmonia]

Can you please update the PR to merge into aws:dev?

Some unit tests need to be updated as well. Please see failures in failed unit tests.