release/dist/qnap: add qnap target builder

Creates new QNAP builder target, which builds go binaries then uses
docker to build into QNAP packages. Much of the docker/script code
here is pulled over from https://github.com/tailscale/tailscale-qpkg,
with adaptation into our builder structures.

The qnap/Tailscale folder contains static resources needed to build
Tailscale qpkg packages, and is an exact copy of the existing folder
in the tailscale-qpkg repo.

Builds can be run with:
```
sudo ./tool/go run ./cmd/dist build qnap
```

Updates tailscale/tailscale-qpkg#135

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

release/dist/qnap/Tailscale/shared/Tailscale.sh

@@ -0,0 +1,50 @@
+#!/bin/sh
+CONF=/etc/config/qpkg.conf
+QPKG_NAME="Tailscale"
+QPKG_ROOT=`/sbin/getcfg ${QPKG_NAME} Install_Path -f ${CONF}`
+QPKG_PORT=`/sbin/getcfg ${QPKG_NAME} Service_Port -f ${CONF}`
+export QNAP_QPKG=${QPKG_NAME}
+set -e
+
+case "$1" in
+  start)
+    ENABLED=$(/sbin/getcfg ${QPKG_NAME} Enable -u -d FALSE -f ${CONF})
+    if [ "${ENABLED}" != "TRUE" ]; then
+        echo "${QPKG_NAME} is disabled."
+        exit 1
+    fi
+    mkdir -p /home/httpd/cgi-bin/qpkg
+    ln -sf ${QPKG_ROOT}/ui /home/httpd/cgi-bin/qpkg/${QPKG_NAME}
+    mkdir -p -m 0755 /tmp/tailscale
+    if [ -e /tmp/tailscale/tailscaled.pid ]; then
+        PID=$(cat /tmp/tailscale/tailscaled.pid)
+        if [ -d /proc/${PID}/ ]; then
+          echo "${QPKG_NAME} is already running."
+          exit 0
+        fi
+    fi
+    ${QPKG_ROOT}/tailscaled --port ${QPKG_PORT} --statedir=${QPKG_ROOT}/state --socket=/tmp/tailscale/tailscaled.sock 2> /dev/null &
+    echo $! > /tmp/tailscale/tailscaled.pid
+    ;;
+
+  stop)
+    if [ -e /tmp/tailscale/tailscaled.pid ]; then
+      PID=$(cat /tmp/tailscale/tailscaled.pid)
+      kill -9 ${PID} || true
+      rm -f /tmp/tailscale/tailscaled.pid
+    fi
+    ;;
+
+  restart)
+    $0 stop
+    $0 start
+    ;;
+  remove)
+    ;;
+
+  *)
+    echo "Usage: $0 {start|stop|restart|remove}"
+    exit 1
+esac
+
+exit 0

release/dist/qnap/Tailscale/shared/ui/.htaccess

@@ -0,0 +1,2 @@
+Options +ExecCGI
+AddHandler cgi-script .cgi

release/dist/qnap/Tailscale/shared/ui/index.cgi

@@ -0,0 +1,5 @@
+#!/bin/sh
+CONF=/etc/config/qpkg.conf
+QPKG_NAME="Tailscale"
+QPKG_ROOT=$(/sbin/getcfg ${QPKG_NAME} Install_Path -f ${CONF} -d"")
+exec "${QPKG_ROOT}/tailscale" --socket=/tmp/tailscale/tailscaled.sock web --cgi --prefix="/cgi-bin/qpkg/Tailscale/index.cgi/"