Add a pre-deploy hook

Useful for checking the status of CI before deploying. Doing this at
this point in the deployment maximises the parallelisation of building
and running CI.

test/integration/docker/deployer/app/.mrsk/hooks/pre-deploy

@@ -0,0 +1,3 @@
+#!/bin/sh
+echo "Deployed!"
+mkdir -p /tmp/${TEST_ID} && touch /tmp/${TEST_ID}/pre-deploy