buffet: Add flag to disable XMPP support

As a temporary work around to major source of flake in tests, allow
disabling XMPP support in tests.

BUG=brillo:769
TEST=FEATURES="test" USE="clang asan" emerge-gizmo buffet && \
     FEATURES="test" emerge-gizmo buffet

Change-Id: I41ca92bb77b77132c1a20c7018b0ce737b69cf60
Reviewed-on: https://chromium-review.googlesource.com/264392
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
diff --git a/buffet/manager.cc b/buffet/manager.cc
index 31115b7..00c5ad2 100644
--- a/buffet/manager.cc
+++ b/buffet/manager.cc
@@ -48,6 +48,7 @@
 void Manager::RegisterAsync(const base::FilePath& config_path,
                             const base::FilePath& state_path,
                             const base::FilePath& test_definitions_path,
+                            bool xmpp_enabled,
                             const AsyncEventSequencer::CompletionAction& cb) {
   command_manager_ =
       std::make_shared<CommandManager>(dbus_object_.GetObjectManager());
@@ -71,6 +72,7 @@
           std::move(config),
           chromeos::http::Transport::CreateDefault(),
           std::move(state_store),
+          xmpp_enabled,
           base::Bind(&Manager::OnRegistrationStatusChanged,
                      base::Unretained(this))));
   device_info_->Load();