MDEV-33582 Add more warnings to be able to better diagnose network issues

Warnings are added to net_server.cc when
global_system_variables.log_warnings >= 4.

When the above condition holds then:
- All communication errors from net_serv.cc is also written to the
  error log.
- In case of a of not being able to read or write a packet, a more
  detailed error is given.

Other things:
- Added detection of slaves that has hangup to Ack_receiver::run()
- vio_close() is now first marking the socket closed before closing it.
  The reason for this is to ensure that the connection that gets a read
  error can check if the reason was that the socket was closed.
- Add a new state to vio to be able to detect if vio is acive, shutdown or
  closed. This is used to detect if socket is closed by another thread.
- Testing of the new warnings is done in rpl_get_lock.test
- Suppress some of the new warnings in mtr to allow one to run some of
  the tests with -mysqld=--log-warnings=4. All test in the 'rpl' suite
  can now be run with this option.
 - Ensure that global.log_warnings are restored at test end in a way
   that allows one to use mtr --mysqld=--log-warnings=4.

Reviewed-by: <serg@mariadb.org>,<brandon.nesterenko@mariadb.com>

mysql-test/suite/rpl/r/rpl_heartbeat_debug.result

@@ -9,8 +9,6 @@ Variable_name	Slave_heartbeat_period
 Value	60.000
 SET @saved_dbug= @@GLOBAL.debug_dbug;
 SET GLOBAL debug_dbug="+d,simulate_slave_heartbeat_network_error";
-CALL mtr.add_suppression('SET @master_heartbeat_period to master failed with error');
-CALL mtr.add_suppression('Master command COM_REGISTER_SLAVE failed: failed registering on master, reconnecting to try again');
 include/start_slave.inc
 connection master;
 drop table if exists t1;