awscreds fails when run in same shell

[Mark-Simulacrum]

As far as I can tell, the awscreds script will fail to run if you run it again in the same shell (i.e. AWS_SESSION_TOKEN is still set), as that token is no longer valid after 12 hours, but the AWS CLI will continue to use it.

For now I've manually worked around this via unset AWS_SESSION_TOKEN but we should probably aim to do so in the script? Not sure.