multisite: some 'radosgw-admin data sync' commands hang
RGWRemoteDataLog::init_sync_status() and read_sync_status() use their own RGWCoroutinesManager, because RGWCoroutinesManager::run() is not reentrant. The rest api needs to call these functions while the sync thread is in RGWRemoteDataLog::run_sync().
However, those coroutines were still using RGWRemoteDataLog::http_manager, which was sending completions to RGWRemoteDataLog's RGWCoroutinesManager. This prevented the coroutines from waking up when the replies came back, and results in hangs.