Migrate to Cloud SDK slim base image. Fixes #528.
Migrate to Cloud SDK slim base image. Fixes #528.

GoogleCloudPlatform/cloud-builders-community,GoogleCloudPlatform/cloud-builders-community,GoogleCloudPlatform/cloud-builders-community,GoogleCloudPlatform/cloud-builders-community,GoogleCloudPlatform/cloud-builders-community,GoogleCloudPlatform/cloud-builders-community,GoogleCloudPlatform/cloud-builders-community,GoogleCloudPlatform/cloud-builders-community