Support users who run maws -w with no intention of using the CLI credentials

[gene1wood]

If a user runs maws -w to access the web console, and has no intention of using the command line credentials and so they don't subshell (e.g. $(maws -w)) the command, the tool now produces a temporary file that doesn't get cleaned up.

1. Determine if this use case matters or if users don't really do this and instead they just browse to https://aws.sso.mozilla.com/
2. If indeed there's a userbase that has a reason to want to run maws -w outside a subshell, come up with a solution to the leftover temp file.