locator: add function to check if host is local

locator/tablets.hh

@@ -114,6 +114,16 @@ tablet_replica_set replace_replica(const tablet_replica_set& rs, tablet_replica
     return result;
 }
 
+inline
+bool contains(const tablet_replica_set& rs, host_id host) {
+    for (auto replica : rs) {
+        if (replica.host == host) {
+            return true;
+        }
+    }
+    return false;
+}
+
 /// Stores information about a single tablet.
 struct tablet_info {
     tablet_replica_set replicas;