Refactor AWS-CLI aliases.

- Add region alias for configured (profile) region.
- Add metadata-region for outputting the region from the EC2 metadata
service, moved from .bashrc (no longer exported as AWS_DEFAULT_REGION,
not an issue since it could only be used in EC2 instances and not for
local use, it was there mainly as a reminder for me).
- Add ecr-login instead of a shell alias, works the same.