docs/libxl: Introduce CHECKPOINT_END to support migration v2 remus streams
In a remus scenario, libxc will write a CHECKPOINT record, then hand
ownership of the fd to libxl. Libxl then writes any records required
and finishes with a CHECKPOINT_END record, then hands ownership of the
fd back to libxc.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Acked-by: Ian Campbell <Ian.Campbell@citrix.com> CC: Ian Jackson <Ian.Jackson@eu.citrix.com> CC: Wei Liu <wei.liu2@citrix.com>