transaction Staging errors map to query error

Staging of the document into gocbcore transactions the error is reported is
"code":17020,"message":"write error" with cause found existing document: document already exists
 

Improve this as follows:

During implicit or explicit staging:

DocumentNotFound       :   N1QL  KEY_NOT_FOUND 17014

DocumentExists, DocAlreadyInTransaction : N1QL DUPLICATE_KEY 17012

AttemptExpired                       : N1QL Transaction expired 17010

These errors will not include cause from gocbcore transactions.

If the statement is commit:  Commit Transaction error 17007  with cause filled above error