Modifications to error handling in restconf

Modified error handling for read and write Tx to transfer to transfer
RpcError info from ReadFailedException and
TransactionCommitFailedException to the RestconfDocumentedException.

Change-Id: Ifb47f0cdfda5a11d53add9d7ef8fbe50954c0206
Signed-off-by: tpantelis <tpanteli@brocade.com>
Merge "Modifications to error handling in restconf"