[Bugfix] The returned result for transaction rollback should be "OK"

[banmoy]

What type of PR is this：

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Which issues of this PR fixes ：

Fixes #

Problem Summary(Required) ：

According to the doc, the returned response for a successful rollback of transaction stream load should be

{
    "TxnId": 1,
    "Label": "a25eca8b-7b48-4c87-9ea7-0cbdd913e77d",
    "Status": "OK",
    "Message": ""
}

The Status field is OK, but currently TransactionStreamLoader#rollback thinks it's Success, and will treat a successful rollback as a failure.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr will affect users' behaviors
• This pr needs user documentation (for new or modified features or behaviors)
• I have added documentation for my new feature or new function