CA-97435: Don't use Record_util code in Storage_access to convert VDI types to strings.

We should only use Record_util for pretty-printing human-readable
values, not for marshalling data for RPC purposes.

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #972 from johnelse/ca-97435

CA-97435: Don't use Record_util code in Storage_access to convert VDI types to strings.