test: fix handling of start height in generated E2E testnets (#5563)

In #5488 the E2E testnet generator changed to setting explicit `StartAt` heights for initial nodes. This broke the runner, which expected all initial nodes to have `StartAt: 0`, as well as validator set scheduling in the generator. Testnet loading now normalizes initial nodes to have `StartAt: 0`.

This also tweaks waiting for misbehavior heights to only use an additional wait if there actually is any misbehavior in the testnet, and to output information when waiting.

test/e2e/pkg/testnet.go

@@ -151,6 +151,9 @@ func LoadTestnet(file string) (*Testnet, error) {
 			Perturbations:    []Perturbation{},
 			Misbehaviors:     make(map[int64]string),
 		}
+		if node.StartAt == testnet.InitialHeight {
+			node.StartAt = 0 // normalize to 0 for initial nodes, since code expects this
+		}
 		if nodeManifest.Mode != "" {
 			node.Mode = Mode(nodeManifest.Mode)
 		}
@@ -341,7 +344,12 @@ func (n Node) Validate(testnet Testnet) error {
 
 	for height, misbehavior := range n.Misbehaviors {
 		if height < n.StartAt {
-			return fmt.Errorf("misbehavior height %d is before start height %d", height, n.StartAt)
+			return fmt.Errorf("misbehavior height %d is below node start height %d",
+				height, n.StartAt)
+		}
+		if height < testnet.InitialHeight {
+			return fmt.Errorf("misbehavior height %d is below network initial height %d",
+				height, testnet.InitialHeight)
 		}
 		exists := false
 		for possibleBehaviors := range mcs.MisbehaviorList {
@@ -395,6 +403,19 @@ func (t Testnet) IPv6() bool {
 	return t.IP.IP.To4() == nil
 }
 
+// LastMisbehaviorHeight returns the height of the last misbehavior.
+func (t Testnet) LastMisbehaviorHeight() int64 {
+	lastHeight := int64(0)
+	for _, node := range t.Nodes {
+		for height := range node.Misbehaviors {
+			if height > lastHeight {
+				lastHeight = height
+			}
+		}
+	}
+	return lastHeight
+}
+
 // Address returns a P2P endpoint address for the node.
 func (n Node) AddressP2P(withID bool) string {
 	ip := n.IP.String()