Trigger pending chain resolution on routing instance change (and add)

Recent change to treat a service chain as pending if the dest routing
instance doesn't have a VN index causes problems if the instance does
not have an index when it's created.

Also fix issue in service_chain_test that causes occasional failures.
Check if DBEnry returned by DBTable::Find is NULL before dynamic_cast.

Change-Id: I971443345699a7909e5247967916ddff0818f78a
Related-bug: 1500698

src/bgp/routing-instance/service_chaining.cc

@@ -1096,7 +1096,8 @@ bool ServiceChainMgr<T>::ResolvePendingServiceChain() {
 
 template <typename T>
 void ServiceChainMgr<T>::RoutingInstanceCallback(string name, int op) {
-    if (op == RoutingInstanceMgr::INSTANCE_ADD) StartResolve();
+    if (op != RoutingInstanceMgr::INSTANCE_DELETE)
+        StartResolve();
 }
 
 template <typename T>

src/bgp/test/service_chain_test.cc

@@ -600,8 +600,7 @@ class ServiceChainTest : public ::testing::Test {
         return table->Size();
     }
 
-    BgpRoute *RouteLookup(const string &instance_name,
-                              const string &prefix) {
+    BgpRoute *RouteLookup(const string &instance_name, const string &prefix) {
         BgpTable *bgp_table = GetTable(instance_name);
         TableT *table = dynamic_cast<TableT *>(bgp_table);
         EXPECT_TRUE(table != NULL);
@@ -612,12 +611,14 @@ class ServiceChainTest : public ::testing::Test {
         PrefixT nlri = PrefixT::FromString(prefix, &error);
         EXPECT_FALSE(error);
         typename TableT::RequestKey key(nlri, NULL);
-        BgpRoute *rt = dynamic_cast<BgpRoute *>(table->Find(&key));
-        return rt;
+        DBEntry *db_entry = table->Find(&key);
+        if (db_entry == NULL) {
+            return NULL;
+        }
+        return dynamic_cast<BgpRoute *>(db_entry);
     }
 
-    BgpRoute *VerifyRouteExists(const string &instance,
-                                    const string &prefix) {
+    BgpRoute *VerifyRouteExists(const string &instance, const string &prefix) {
         TASK_UTIL_EXPECT_TRUE(RouteLookup(instance, prefix) != NULL);
         BgpRoute *rt = RouteLookup(instance, prefix);
         if (rt == NULL) {
@@ -627,13 +628,11 @@ class ServiceChainTest : public ::testing::Test {
         return rt;
     }
 
-    void VerifyRouteNoExists(const string &instance,
-                                 const string &prefix) {
+    void VerifyRouteNoExists(const string &instance, const string &prefix) {
         TASK_UTIL_EXPECT_TRUE(RouteLookup(instance, prefix) == NULL);
     }
 
-    void VerifyRouteIsDeleted(const string &instance,
-                                  const string &prefix) {
+    void VerifyRouteIsDeleted(const string &instance, const string &prefix) {
         TASK_UTIL_EXPECT_TRUE(RouteLookup(instance, prefix) != NULL);
         BgpRoute *rt = RouteLookup(instance, prefix);
         TASK_UTIL_EXPECT_TRUE(rt->IsDeleted());