Incorporating a fix for GKE 1.19+ (See #444).
Inlined:
Google has removed basic-auth method from within GKE starting version 1.19
This lead the output response of the backend API not to provide basic-auth
data (username and password) anymore.
The current implementation of gcp_container_cluster when generating the kubectl
config file, always set basic-auth data w/o checking if there actually are
available or explicitly provided even when the value are not set/provided
from gcp_container_cluster.
In addition, re-enabling some tests that #444 fixed.
Co-authored-by: Xavier Lamien <laxathom@lxtnow.net>
