[issue] Zeronet ignores tor = always if started through systemd

### Step 1: Please describe your environment

* ZeroNet version: 0.6.2 (3408)
* Operating system: Raspbian Stretch
* Web browser: Waterfox 56.1.0
* Tor status: always
* Opened port: no
* Special configuration:

### Step 2: Describe the problem:
If I start zeronet by a systemd unit on bootup, it doesn't connect to Tor.

#### Steps to reproduce:

1. create a zeronet.service file at /lib/systemd/system/
2. put in this
```
[Unit]
Description=Zeronet daemon
Wants=tor.service
After=network.target tor.service

[Service]
EnvironmentFile=/home/pi/ZeroNet-master/zeronet.conf
ExecStart=/home/pi/ZeroNet-master/zeronet.py --tor always
User=
TimeoutStopSec=30min

[Install]
WantedBy=multi-user.target
```

3. execute
```
sudo systemctl daemon-reload
sudo systemctl enable zeronet.service
sudo reboot
```

#### Observed Results:

It displays this
error message in the top right corner but it's working fine. It just connects to the zeronet without tor and. The errorlog states:
```
[2018-04-14 15:57:15,386] WARNING TorManager Tor controller connect error: error: [Errno 111] Connection refused in TorManager.py line 170 > _socket2.py line 228
[2018-04-14 15:57:15,386] INFO TorManager Starting self-bundled Tor, due to Tor proxy port 127.0.0.1:9050 check error: No connection
```

#### Expected Results:

Zeronet shouldn't establish any connection when Tor isn't reachable and should try to reconnect to Tor if it wasn't available during the initialization.

从 TorManager.py 第 170 行附近以及由 systemd 单元调用的 zeronet.py 启动路径开始。使用提供的服务配置重现启动时的故障，然后跟踪 Tor 可用性的处理逻辑。完成的标准是：Tor 不可用时，ZeroNet 不回退到非 Tor 连接，并在 Tor 恢复可访问后重试。

由索引模型根据 Issue 内容生成。