docs/k8s: make run.sh handle SIGINT

It was previously using jobcontrol to achieve this, but that apparently
doesn't work when there is no tty. This makes it so that it directly
handles SIGINT and SIGTERM and passes it on to tailscaled. I tested this
works on a Digital Ocean K8s cluster.

Fixes #5512

Signed-off-by: Maisem Ali <maisem@tailscale.com>
(cherry picked from commit 060ecb010f)

docs/k8s/run.sh

@@ -4,8 +4,6 @@
 
 #! /bin/sh
 
-set -m # enable job control
-
 export PATH=$PATH:/tailscale/bin
 
 TS_AUTH_KEY="${TS_AUTH_KEY:-}"
@@ -60,8 +58,16 @@ if [[ ! -z "${TS_TAILSCALED_EXTRA_ARGS}" ]]; then
   TAILSCALED_ARGS="${TAILSCALED_ARGS} ${TS_TAILSCALED_EXTRA_ARGS}"
 fi
 
+handler() {
+  echo "Caught SIGINT/SIGTERM, shutting down tailscaled"
+  kill -s SIGINT $PID
+  wait ${PID}
+}
+
 echo "Starting tailscaled"
 tailscaled ${TAILSCALED_ARGS} &
+PID=$!
+trap handler SIGINT SIGTERM
 
 UP_ARGS="--accept-dns=${TS_ACCEPT_DNS}"
 if [[ ! -z "${TS_ROUTES}" ]]; then
@@ -82,4 +88,5 @@ if [[ ! -z "${TS_DEST_IP}" ]]; then
   iptables -t nat -I PREROUTING -d "$(tailscale --socket=/tmp/tailscaled.sock ip -4)" -j DNAT --to-destination "${TS_DEST_IP}"
 fi
 
-fg
+echo "Waiting for tailscaled to exit"
+wait ${PID}