When libvirtd exits it is leaving UNIX domain sockets on
the filesystem. These need to be removed.

The qemudInitPaths() method has signficant code churn to
switch from using a pre-allocated buffer on the stack, to
dynamically allocating on the heap.

* daemon/libvirtd.c, daemon/libvirtd.h: Store a reference
  to the UNIX domain socket path and unlink it on shutdown