AIAP: Keep containers alive in successful runs

Currently the task containers will reach a conclusive state (success or
failure), and will promptly stop running. This creates the following
problems:
  1. In the case of failure, a user doesn't have the ability to exec into
     the container for debugging purposes.
  2. In the case a success, the readiness probe for each task container
     will begin to fail. This happens because readiness is defined by
     the existence of a file; if the container stops running, the file
     no longer exists.

This change provides a solution to the 2nd bullet, keeping the container
alive in case of success.

Change-Id: Iae432caada3d2a338493b1534da72957808185d2

tools/airship-in-a-pod/artifact-setup/assets/entrypoint.sh

@@ -58,3 +58,6 @@ fi
 
 success=true
 /signal_complete artifact-setup
+
+# Keep the container running for debugging/monitoring purposes
+sleep infinity

tools/airship-in-a-pod/infra-builder/assets/entrypoint.sh

@@ -34,3 +34,6 @@ ansible-playbook -v /opt/ansible/playbooks/build-infra.yaml \
 
 success=true
 /signal_complete infra-builder
+
+# Keep the container running for debugging/monitoring purposes
+sleep infinity

tools/airship-in-a-pod/runner/assets/entrypoint.sh

@@ -81,3 +81,6 @@ fi
 
 success=true
 /signal_complete runner
+
+# Keep the container running for debugging/monitoring purposes
+sleep infinity