Use "git cherry-pick" for implementing copy/paste of commits

We do this because
- it's closer to what you would do on the command line
- it simplifies the code a bit
- it will allow us to support cherry-picking merge commits.

pkg/integration/tests/cherry_pick/cherry_pick_during_rebase.go

@@ -75,8 +75,8 @@ var CherryPickDuringRebase = NewIntegrationTest(NewIntegrationTestArgs{
 			}).
 			Lines(
 				Contains("pick  CI two"),
-				Contains("pick  CI three"),
-				Contains("      CI <-- YOU ARE HERE --- one"),
+				Contains("      CI <-- YOU ARE HERE --- three"),
+				Contains("      CI one"),
 				Contains("      CI base"),
 			).
 			Tap(func() {