Arista eAPI getUptime Fixed

Corrected getUptime() in eapi.py to handle getting the correct uptime.

Two samples with different values

```bash
$ python main.py -i 192.168.31.21 -m arista -n 'SW1' -f getUptime
22:29
```
```bash
$ python main.py -i 10.17.31.51 -m arista -n 'SW1' -f getUptime
41 min
```