add a check that the refresh <= the ttl duration

The logic depends on the refresh being smaller than or equal to the
TTL so add a startup assertion that it is configured that way.

Also update all test cases that override the ttl to also override
the refresh interval to avoid hitting this assertion.

go/vt/discovery/tablet_stats_cache_wait_test.go

@@ -54,7 +54,8 @@ func (a TargetArray) Less(i, j int) bool {
 func TestFindAllKeyspaceShards(t *testing.T) {
 	ctx := context.Background()
 	ts := memorytopo.NewServer("cell1", "cell2")
-	flag.Set("srv_topo_cache_ttl", "0s") // No caching values
+	flag.Set("srv_topo_cache_ttl", "0s")     // No caching values
+	flag.Set("srv_topo_cache_refresh", "0s") // No caching values
 	rs := srvtopo.NewResilientServer(ts, "TestFindAllKeyspaceShards")
 
 	// No keyspace / shards.

go/vt/srvtopo/resilient_server.go

@@ -164,6 +164,10 @@ type srvKeyspaceEntry struct {
 // NewResilientServer creates a new ResilientServer
 // based on the provided topo.Server.
 func NewResilientServer(base *topo.Server, counterPrefix string) *ResilientServer {
+	if *srvTopoCacheRefresh > *srvTopoCacheTTL {
+		log.Fatalf("srv_topo_cache_refresh must be less than or equal to srv_topo_cache_ttl")
+	}
+
 	return &ResilientServer{
 		topoServer:   base,
 		cacheTTL:     *srvTopoCacheTTL,

test/utils.py

@@ -550,6 +550,7 @@ def start(self, cell='test_nj', retry_count=2,
         '-retry-count', str(retry_count),
         '-log_dir', environment.vtlogroot,
         '-srv_topo_cache_ttl', cache_ttl,
+        '-srv_topo_cache_refresh', cache_ttl,
         '-tablet_protocol', protocols_flavor().tabletconn_protocol(),
         '-stderrthreshold', get_log_level(),
         '-normalize_queries',
@@ -799,6 +800,7 @@ def start(self, cell='test_nj', retry_count=2,
         '-retry-count', str(retry_count),
         '-log_dir', environment.vtlogroot,
         '-srv_topo_cache_ttl', cache_ttl,
+        '-srv_topo_cache_refresh', cache_ttl,
         '-tablet_protocol', protocols_flavor().tabletconn_protocol(),
         '-gateway_implementation', vtgate_gateway_flavor().flavor(),
     ]