Update failover e2e test

As part of the move from failover to switchover the output message from
the `pgo failover` command was updated. This change updates the test to
account for the new output message.

Author: jmckulk

testing/pgo_cli/cluster_failover_test.go

@@ -68,7 +68,7 @@ func TestClusterFailover(t *testing.T) {
 						"--target="+before[0].Labels["deployment-name"], "--no-prompt",
 					).Exec(t)
 					require.NoError(t, err)
-					require.Contains(t, output, "created")
+					require.Contains(t, output, "success")
 
 					replaced := func() bool {
 						after := replicaPods(t, namespace(), cluster())