capture_replay_tests: Fix repository path retrieval. Use relation to retrieve angle repository path. The previous way of detecting the root repository folder failed to detect a correct path if the angle directory was in a path that contained the string angle. e.g. `/home/user/code/angle/angle` Other paths that would fail with the current implementation: `/home/user/my-angle-workspace/angle` `/home/tangled/workspace/angle/` `/home/user/code/angle-android` This way the path is constructed with the known relation of the script path inside the repository. Another advantage of this way is that the `angle` repository could be checked out with a different name. The disadvantage of this method is that whenever the script was moved, the relative path must be updated. Bug: angleproject:5645 Change-Id: I9a56aeba449b248273087382adceb0d6fba5a494 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2715323 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>