token_metadata: get_endpoint_for_host_id -> get_endpoint_for_host_id_if_known

This commit fixes an inconsistency in method names:
get_host_id and get_host_id_if_known are
(internal_error, returns null), but there was only
one method for the opposite conversion - get_endpoint_for_host_id,
and it returns null. In this commit we change it to on_internal_error
if it can't find the argument and add another method
get_endpoint_for_host_id_if_known which returns null in this case.

We can't use get_endpoint_for_host_id/get_host_id
in host_id_or_endpoint::resolve since it's called
from storage_service::parse_node_list
-> token_metadata::parse_host_id_and_endpoint,
and exceptions are caught and handled in
`storage_service::parse_node_list`.

db/view/view.cc

@@ -2579,7 +2579,7 @@ future<bool> check_view_build_ongoing(db::system_distributed_keyspace& sys_dist_
     return sys_dist_ks.view_status(ks_name, cf_name).then([&tm] (view_statuses_type&& view_statuses) {
         return boost::algorithm::any_of(view_statuses, [&tm] (const view_statuses_type::value_type& view_status) {
             // Only consider status of known hosts.
-            return view_status.second == "STARTED" && tm.get_endpoint_for_host_id(view_status.first);
+            return view_status.second == "STARTED" && tm.get_endpoint_for_host_id_if_known(view_status.first);
         });
     });
 }