Do not fail GCP auth when GOOGLE_APPLICATION_CREDENTIALS is not found

[pablomh]

Auth could have been set up using the Google Cloud CLI:

• gcloud init
• gcloud auth application-default login

[paigerube14]

Got this error when not setting the google application credentials.

Also would be good to add this to the docs as an alternative way to configure the cloud for this scenario

2024-10-07 13:54:51,605 [INFO] Starting node_stop_start_scenario injection
2024-10-07 13:54:51,605 [INFO] stop scenario
2024-10-07 13:54:51,605 [INFO] Starting node_stop_scenario injection
2024-10-07 13:54:51,606 [ERROR] Failed to stop node instance. Encountered following exception: 'GCP' object has no attribute 'project'. Test Failed

[chaitanyaenr]

Got this error when not setting the google application credentials.

cc: @pablomh

[pablomh]

I've changed the status to DRAFT while I figure out how to avoid @paigerube14 problem. The reason I didn't spot it is because I've been testing this code using the google.auth Python API which sets project using:

credentials, project = google.auth.default()

[pablomh]

Will close in favor of #723.