memory leak resolve for dispatcher (#4597)

include/osquery/dispatcher.h

@@ -115,7 +115,7 @@ class InternalRunnable : private boost::noncopyable,
 
 /// An internal runnable used throughout osquery as dispatcher services.
 using InternalRunnableRef = std::shared_ptr<InternalRunnable>;
-using InternalThreadRef = std::unique_ptr<std::thread>;
+using InternalThreadRef = std::shared_ptr<std::thread>;
 
 /**
  * @brief Singleton for queuing asynchronous tasks to be executed in parallel

osquery/dispatcher/dispatcher.cpp

@@ -75,7 +75,7 @@ Status Dispatcher::addService(InternalRunnableRef service) {
     return Status(1, "Cannot add service, dispatcher is stopping");
   }
 
-  auto thread = std::make_unique<std::thread>(
+  auto thread = std::make_shared<std::thread>(
       std::bind(&InternalRunnable::run, &*service));
 
   DLOG(INFO) << "Adding new service: " << service->name() << " ("