Modify resolving sso credential logic

[wty-Bryant]

Modify resolving sso credential logic to fix stack overflow bug while configuring shared config profile via env var. Resolves #4912 . The manual test of fixed sso credential resolve logic follows steps below:

1. run the sso login flow with the AWS CLI
2. set env variable AWS_SDK_LOAD_CONFIG=TRUE
3. set env variable AWS_PROFILE=<some_profile_in_config_using_same_sso>
4. create session with session.NewSession(), then use new session to create S3 client
5. use the access token generated, call S3 List Buckets on the configured AWS account
6. when the access token expires, re-call S3 List buckets and see it succeed with an updated expiration in the SSO cached token