Use self update ready entrypoint (#99)

* Use self update ready entrypoint

* Add --once support for runsvc.sh

Run `cd runner; NAME=$DOCKER_USER/actions-runner TAG=dev make docker-build docker-push`,
`kubectl apply -f release/actions-runner-controller.yaml`,
then update the runner image(not the controller image) by updating e.g. `Runner.Spec.Image` to `$DOCKER_USER/actions-runner:$TAG`, for testing.

Co-authored-by: Yusuke Kuoka <ykuoka@gmail.com>

runner/patched/runsvc.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+
+# convert SIGTERM signal to SIGINT
+# for more info on how to propagate SIGTERM to a child process see: http://veithen.github.io/2014/11/16/sigterm-propagation.html
+trap 'kill -INT $PID' TERM INT
+
+if [ -f ".path" ]; then
+    # configure
+    export PATH=`cat .path`
+    echo ".path=${PATH}"
+fi
+
+# insert anything to setup env when running as a service
+
+# run the host process which keep the listener alive
+./externals/node12/bin/node ./bin/RunnerService.js $* &
+PID=$!
+wait $PID
+trap - TERM INT
+wait $PID