Stop the IO service when we're shutting down with force=true

This will cause the http::Client to not block & exit immediately
when we're calling Client::close

lib/http/client.cpp

@@ -40,15 +40,17 @@ Client::set_server(const std::string &server)
 void
 Client::close(bool force)
 {
+        // We close all open connections.
+        if (force) {
+                shutdown();
+                ios_.stop();
+        }
+
         // Destroy work object. This allows the I/O thread to
         // exit the event loop when there are no more pending
         // asynchronous operations.
         work_.reset();
 
-        // We close all open connections.
-        if (force)
-                shutdown();
-
         // Wait for the worker threads to exit.
         thread_group_.join_all();
 }