'aws2 sso login' should not open SSO login page on browser if current security token is still valid

**Is your feature request related to a problem? Please describe.**
I have setup my iTerm2 profile to run 'aws2 sso login' when I open terminal, as I want my terminal to be setup automatically to accept **kubectl** commands. But each time I get redirected to a browser, even when my temporary credentials and token is currently active.

**Describe the solution you'd like**
Don't open browser if my temporary credentials are valid and active.

**Describe alternatives you've considered**
No alternative