[launcher] Change base COS image to cos-113-lts (google#467)

Moving base image to a more stable and supportive release track.

Signed-off-by: Jiankun Lu <[email protected]>

launcher/cloudbuild.yaml

@@ -1,8 +1,6 @@
 substitutions:
-  # using this base image for now, because there is an issue causing the newest COS dev
-  # image not booting with cs.
-  '_BASE_IMAGE': 'cos-dev-117-18374-0-0' # Use a stable COS version to avoid CS image build issues
-  '_BASE_IMAGE_FAMILY': 'cos-dev' # base image family
+  '_BASE_IMAGE': '' # an empty base image means the build will use the latest image in '_BASE_IMAGE_FAMILY'
+  '_BASE_IMAGE_FAMILY': 'cos-113-lts' # base image family
   '_OUTPUT_IMAGE_PREFIX': 'confidential-space'
   '_OUTPUT_IMAGE_SUFFIX': ''
   '_OUTPUT_IMAGE_FAMILY': ''