Chutney tries to convert empty pid string to integer
In the `getPid()` function, Chutney reads the pid from a file and converts it to an integer.
```
if not os.path.exists(pidfile):
return None
with open(pidfile, 'r') as f:
return int(f.read())
```
This can result in the following error:
```
ValueError: invalid literal for int() with base 10: ''
```
PR incoming...
issue