SMAPIv2 expects valid dates

We conventionally use Jan 1 1970 to mean "it never happened"

Signed-off-by: David Scott <dave.scott@eu.citrix.com>

Author: David Scott

main.ml

@@ -102,7 +102,7 @@ let vdi_of_volume x =
   ty = "";
   metadata_of_pool = "";
   is_a_snapshot = false;
-  snapshot_time = "";
+  snapshot_time = "19700101T00:00:00Z";
   snapshot_of = "";
   read_only = not x.Storage.V.Types.read_write;
   virtual_size = x.Storage.V.Types.virtual_size;