simplewallet: don't ask about mining when running a command line

This is likely to be done via a script

src/simplewallet/simplewallet.cpp

@@ -4087,6 +4087,8 @@ bool simple_wallet::init(const boost::program_options::variables_map& vm)
 
   m_wallet->callback(this);
 
+  bool skip_check_backround_mining = !command_line::get_arg(vm, arg_command).empty();
+  if (!skip_check_backround_mining)
     check_background_mining(password);
 
   if (welcome)