`aws configure get` does not work if a `credential_process` is used

Reproduce:

1. Have a (working) config like:
> ```ini
> [profile ojford]
> credential_process=/usr/local/bin/get-ojfords-creds
> ```

2. Verify (obscured & tabulated values) with: `aws configure list`
2. Run: `aws configure get aws_access_key_id`

Expected: Unobscured & untabulated value on stdout, exit code 0.
Actual: No output, exit code 1.