Flaky test reporter and retryer won't work well for duplicated repo names

When flaky test reporter generate report files, the file name will only contain the repo name, see https://github.com/knative/test-infra/blob/master/tools/flaky-test-reporter/jsonreport/jsonreport.go#L78, and flaky test retryer will only get the report with the repo name. This normally works well, but will have problems for sure if there are duplicated repo names under different orgs.

The fix would be also appending the org name in the name of the report artifact.

/bug

Start in tools/flaky-test-reporter/jsonreport/jsonreport.go around line 78, then trace how the flaky test retryer selects report files. Ensure report artifacts and retryer lookup distinguish repositories with the same name under different organizations, and verify the reporter and retryer tests cover duplicated repo names.

Written by the indexing model from the issue text.