src: replace last_component() with g_path_get_basename()

src: replace last_component() with g_path_get_basename()

The last_component() method is a GNULIB custom function
that returns a pointer to the base name in the path.
This is similar to g_path_get_basename() but without the
malloc. The extra malloc is no trouble for libvirt's
needs so we can use g_path_get_basename().

Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>