Add total MH/s across all machines to output

The new output now looks like this:

```
rig-instance         GPU status load working-in-pool           worker               MH/s temp   fan fan% rejects hwerr mspd gspd int
------------------------------------------------------------------------------------------------------------------------------------
192.168.111.45:4028   0  Alive   64% usa.wemineltc.com:3334    flamingpoop.miner45  0.68  86C  3030 100%   0.15%     0 1500 1050  13
192.168.111.45:4028   1  Alive   99% usa.wemineltc.com:3334    flamingpoop.miner45  0.74  73C  2989  82%   0.27%     0 1500 1050  13
192.168.111.45:4028   2  Alive   64% usa.wemineltc.com:3334    flamingpoop.miner45  0.69  82C  3014  85%   0.08%     0 1500 1050  13
192.168.111.45:4028   3  Alive   99% usa.wemineltc.com:3334    flamingpoop.miner45  0.69  72C  1734  46%   0.55%     0 1500 1050  13
192.168.111.127:4028  0  Alive   99% usa.wemineltc.com:3334    flamingpoop.miner2   0.41  82C    -1 100%   2.35%     4 1250  800  20
192.168.111.127:4028  1  Alive   99% usa.wemineltc.com:3334    flamingpoop.miner2   0.41  75C    -1  85%   2.23%     4 1250  800  20
192.168.111.126:4028  0  Alive   99% usa.wemineltc.com:3334    flamingpoop.miner3   0.39  68C    -1   0%   2.08%    10 1250  800  20
------------------------------------------------------------------------------------------------------------------------------------
Total MH/s across all machines: 4.01
```