fix SystemV init script template for debian packaging

For processes that manage their own pid file, they should define the `PIDFILE` variable (sourced either through `/etc/default/…` or `/etc/sysconfig/…`). Otherwise, if undefined, this script will capture the pid and write it to `/var/run/${{app_name}}/running.pid`.

This commit is related to 45bc5db that implements the same logic for rpm packaging

src/main/resources/com/typesafe/sbt/packager/archetypes/java_server/systemloader/systemv/start-debian-template

@@ -18,7 +18,12 @@ source /lib/lsb/init-functions
 # $JAVA_OPTS used in $RUN_CMD wrapper
 export JAVA_OPTS
 
-PIDFILE=/var/run/${{app_name}}/running.pid
+# If program manages its own PID file then it
+# should declare its location in PIDFILE
+if [ -z "$PIDFILE" ]; then
+    create_pidfile=true
+    PIDFILE=/var/run/${{app_name}}/running.pid
+fi
 
 if [ -z "$DAEMON_USER" ]; then
     DAEMON_USER=${{daemon_user}}
@@ -35,7 +40,11 @@ RUN_CMD="${{chdir}}/bin/${{exec}}"
 start_daemon() {
     log_daemon_msg "Starting" "${{app_name}}"
     [ -d "/var/run/${{app_name}}" ] || install -d -o "$DAEMON_USER" -g "$DAEMON_GROUP" -m755 "/var/run/${{app_name}}"
-    start-stop-daemon --background --chdir ${{chdir}} --chuid "$DAEMON_USER" --make-pidfile --pidfile "$PIDFILE" --startas "$RUN_CMD" --start -- $RUN_OPTS
+    if [ "$create_pidfile" = true ]; then
+        start-stop-daemon --background --chdir ${{chdir}} --chuid "$DAEMON_USER" --make-pidfile --pidfile "$PIDFILE" --startas "$RUN_CMD" --start -- $RUN_OPTS
+    else
+        start-stop-daemon --background --chdir ${{chdir}} --chuid "$DAEMON_USER" --pidfile "$PIDFILE" --startas "$RUN_CMD" --start -- $RUN_OPTS
+    fi
     log_end_msg $?
 }