The vfkit client socket is not deleted when the VM terminates from within the guest

[nirs]

% vfkit --version
vfkit version: v0.6.0

To reproduce:

1. Start vfkit with --virtio-net,unixSocketPath=/path/vmnet.sock
2. It creates the client socket at /path/vfkit-190b-e485.sock
3. Login to the VM via serial console and run:

   sudo poweroff
   

4. vfkit terminates:

   $ sudo poweroff
   ubuntu@example-vm:~$ INFO[0028] VM is stopped                                 
   

Socket is not removed.

When interrupting vfkit, the socket is removed:

example-vm login: INFO[0014] captured interrupt, calling exit handlers and exiting.. 

This does not affect the functionality, but since the socket includes a pid, we get new socket per each vfkit run.

The code includes this 5 months old comment:

// FIXME: need to remove localSocketPath at process exit