The listener script should live in cfme_tests/scripts, rather than cfme_tests/tests/common

`os.getcwd` isn't reliable for trying to get at locations relative to a running script, but we've got `__file__` and `py.path` available to us. Here's a snippet that should work any time, anywhere:

```python
from py.path import local
script_path = local(__file__).new(basename='../scripts/listener.py')
```

script_path will be a LocalPath instance, but will do the right thing when coerced to a string type.