The internal glue layer for the new pubic API

* src/driver.h: Define internal driver API contract
* src/libvirt.c, src/libvirt_public.syms: Wire up public
  API to internal driver API
* src/esx/esx_driver.c, src/lxc/lxc_driver.c, src/opennebula/one_driver.c,
  src/openvz/openvz_driver.c, src/phyp/phyp_driver.c,
  src/qemu/qemu_driver.c, src/remote/remote_driver.c,
  src/test/test_driver.c, src/uml/uml_driver.c, src/vbox/vbox_tmpl.c,
  src/xen/xen_driver.c: Stub new entry point