Support Cloud Pak For Data (CP4D) Authentication

[rgeorgi]

Cloud Pak For Data (CP4D) uses a slightly different authentication mechanism than the standard IAM Token. This PR adds the BearerTokenAuthenticator from ibm_cloud_sdk_core to support authentication via the user-based bearer token CP4D users can find in their instances' service details page.

I've add PR 174 that offers a solution for this, adding an --auth-type arg to the commandline programs and an auth_type key to the config.ini file to specify this (non-default) behavior.