Perform cleanup before starting net_probe.py

If net_probe.py fails for unknown reason,
daemon process will hang there forever and next
net_probe.py run will fail with socket.bind error

Change-Id: I1f5889d59dc60aa374fdf3f9dd8e3e5e7c0a115b
Closes-Bug: #1259935
Merge "Perform cleanup before starting net_probe.py"