Change post_detach_hook to post_deactivate_hook

Previously the `post_detach_hook` was run after the VDI is detached on
the source VM, which is at the very end of the SXM, where the source VM
is shutdown. However, the job of `post_detach_hook` is to call
`Remote.receive_finalize` which will destroy the mirroring datapath.
This should have been called as soon as we deactivate the datapath on
the source VM, at which point the source VM will stop writing using that
datapath. This commit changes `post_detach_hook` to
`post_deactivate_hook` and moves its calling locations accordingly.

Signed-off-by: Vincent Liu <[email protected]>

Author: Vincent-lau

ocaml/xapi/storage_migrate.ml

@@ -1320,7 +1320,7 @@ let pre_deactivate_hook ~dbg:_ ~dp:_ ~sr ~vdi =
              s.failed <- true
      )
 
-let post_detach_hook ~sr ~vdi ~dp:_ =
+let post_deactivate_hook ~sr ~vdi ~dp:_ =
   let open State.Send_state in
   let id = State.mirror_id_of (sr, vdi) in
   State.find_active_local_mirror id

ocaml/xapi/storage_smapiv1_wrapper.ml

@@ -422,10 +422,10 @@ functor
               | Vdi_automaton.Deactivate ->
                   Storage_migrate.pre_deactivate_hook ~dbg ~dp ~sr ~vdi ;
                   Impl.VDI.deactivate context ~dbg ~dp ~sr ~vdi ~vm ;
+                  Storage_migrate.post_deactivate_hook ~sr ~vdi ~dp ;
                   vdi_t
               | Vdi_automaton.Detach ->
                   Impl.VDI.detach context ~dbg ~dp ~sr ~vdi ~vm ;
-                  Storage_migrate.post_detach_hook ~sr ~vdi ~dp ;
                   vdi_t
             in
             Sr.add_or_replace vdi new_vdi_t sr_t ;