roachtest: fix cluster-init

This is an edulcorated backport of cockroachdb#69940, which cannot be backported
as-is due to severe roachtest infra changes.

Release justification: test-only changes

Release note: None

pkg/cmd/roachtest/cluster_init.go

@@ -44,6 +44,20 @@ func runClusterInit(ctx context.Context, t *test, c *cluster) {
 		c.Wipe(ctx)
 
 		func() {
+			// At the end of each iteration, wipe the cluster if the test
+			// has succeeded.  This is useful because the `roachprod
+			// monitor` command at the end seems to be confused by `start`
+			// commands that were not issued by c.Start(). Wipe the data
+			// directory at the end before the test function terminates
+			// ensures that the monitor check does not run.
+			defer func() {
+				// Defers are run unconditionally, even during a Fatal call.
+				if !t.Failed() {
+					c.l.Printf("wiping cluster after test success")
+					c.Wipe(ctx)
+				}
+			}()
+
 			var g errgroup.Group
 			for i := 1; i <= c.spec.NodeCount; i++ {
 				i := i