gossip: Improve get_live_token_owners and get_unreachable_token_owners

The get_live_token_owners returns the nodes that are part of the ring
and live.

The get_unreachable_token_owners returns the nodes that are part of the ring
and is not alive.

The token_metadata::get_all_endpoints returns nodes that are part of the
ring.

The patch changes both functions to use the more authoritative source to
get the nodes that are part of the ring and call is_alive to check if
the node is up or down. So that the correctness does not depend on
any derived information.

This patch fixes a truncate issue in storage_proxy::truncate_blocking
where it calls get_live_token_owners and get_unreachable_token_owners to
decide the nodes to talk with for truncate operation. The truncate
failed because incorrect nodes were returned.

Fixes scylladb#10296
Fixes scylladb#11928

gms/gossiper.cc

@@ -1020,21 +1020,22 @@ std::set<inet_address> gossiper::get_live_members() const {
 
 std::set<inet_address> gossiper::get_live_token_owners() const {
     std::set<inet_address> token_owners;
-    for (auto& member : get_live_members()) {
-        auto es = get_endpoint_state_for_endpoint_ptr(member);
-        if (es && !is_dead_state(*es) && get_token_metadata_ptr()->is_member(member)) {
-            token_owners.insert(member);
+    auto normal_token_owners = get_token_metadata_ptr()->get_all_endpoints();
+    for (auto& node: normal_token_owners) {
+        if (is_alive(node)) {
+            token_owners.insert(node);
         }
     }
     return token_owners;
+
 }
 
 std::set<inet_address> gossiper::get_unreachable_token_owners() const {
     std::set<inet_address> token_owners;
-    for (auto&& x : _unreachable_endpoints) {
-        auto& endpoint = x.first;
-        if (get_token_metadata_ptr()->is_member(endpoint)) {
-            token_owners.insert(endpoint);
+    auto normal_token_owners = get_token_metadata_ptr()->get_all_endpoints();
+    for (auto& node: normal_token_owners) {
+        if (!is_alive(node)) {
+            token_owners.insert(node);
         }
     }
     return token_owners;