Collate test_result bundles in multi_scan

Overview

This release adds a new action, collate_test_result_bundles which will collate the test_result bundles into one final test_result bundle. The multi_scan action has been updated to use this new action in order to collate the test_result bundles together into one result bundle.

Details

In the TestSummaries.plist file, Tests in older test_result bundles will be moved to a PreviousTests entry so that one can review what failed in previous runs of multi_scan.

Screenshot images in the Attachments directory are simply added to the merged Attachments directory as they are uniquely named.

Diagnostics are simply copied into the final test_result bundle as each test run has a uniquely named output directory.

xcactivitylogs are gunzipped, concatenated, and gzipped.