Only run SR.create compat fallback for PVS version of SM scripts

This makes the code stricter - previously we ran the compat code for all
versions, and as a result we accepted an empty response, even from newer
versions.

This change will make the code stricter, and probably safer, now we'll
fail if the newer storage scripts return an invalid, empty response from
SR.create.

Signed-off-by: Gabor Igloi <[email protected]>

Author: gaborigloi

main.ml

@@ -196,11 +196,15 @@ end = struct
 
   let sr_create device_config =
     compat_uri device_config >>>= fun compat_in ->
-    let compat_out rpc =
-      (* The PVS version will return nothing *)
-      if rpc = R.Null then
-        Rpcmarshal.marshal Xapi_storage.Control.typ_of_configuration device_config
-      else rpc
+    let compat_out =
+      if !V.version = Some pvs_version then begin
+        fun rpc ->
+          (* The PVS version will return nothing *)
+          if rpc = R.Null then
+            Rpcmarshal.marshal Xapi_storage.Control.typ_of_configuration device_config
+          else rpc
+      end
+      else id
     in
     return (Ok (device_config, compat_in, compat_out))