[   0.0] Examining the guest ...
virt-customize: error: libguestfs error: could not create appliance through 
libvirt.

Try running qemu directly without libvirt using this environment variable:
export LIBGUESTFS_BACKEND=direct

Original error from libvirt: Cannot recv data: Connection reset by peer 
[code=38 int1=104]

If reporting bugs, run virt-customize with debugging enabled and include 
the complete output:

  virt-customize -v -x [...]