TT#19300 Fix ngcp-panel start race condition on server boot

The old code removed PID file before the check of starting ngcp-panel,
as a result in the worst case it removes PIDFILE for 'just' started ngcp-panel.

We should ensure no ngcp-panel is being started before removing PIDFILE.

Change-Id: I10e601639b81d5837d132ee78a5945419fde81d5

debian/ngcp-panel.init

@@ -77,8 +77,8 @@ _start() {
     log_end_msg 0
     exit 0
   fi
-  rm -f $PIDFILE 2>/dev/null
   check_for_ongoing_startup || return 0
+  rm -f "$PIDFILE" 2>/dev/null
    # shellcheck disable=SC2086
   start-stop-daemon --start --quiet \
         --pidfile $PIDFILE \