Add --follow-instant-failovers option to MariaDB CLI

This option is ENABLED by default.

The `main.mysqld--help` MTR test is updated as well, to reflect the addition
of this option to the `mysqld --help` output.

All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license. I am contributing on behalf of my employer Amazon Web
Services, Inc.

client/mysql.cc

@@ -248,7 +248,8 @@ static my_bool ignore_errors=0,wait_flag=0,quick=0,
  default_pager_set= 0, opt_sigint_ignore= 0,
  auto_vertical_output= 0, show_query_cost= 0,
  show_warnings= 0, executing_query= 0,
- ignore_spaces= 0, opt_binhex= 0, opt_progress_reports;
+ ignore_spaces= 0, opt_binhex= 0, opt_progress_reports,
+ opt_follow_instant_failovers= 1;
 static my_bool debug_info_flag, debug_check_flag, batch_abort_on_error;
 static my_bool column_types_flag;
 static my_bool preserve_comments= 0;
@@ -1503,6 +1504,8 @@ static bool do_connect(MYSQL *mysql, const char *host, const char *user,
  if (opt_secure_auth)
  mysql_options(mysql, MYSQL_SECURE_AUTH, (char *) &opt_secure_auth);
  SET_SSL_OPTS_WITH_CHECK(mysql);
+ mysql_options(mysql,MARIADB_OPT_FOLLOW_INSTANT_FAILOVERS,
+ (char*)&opt_follow_instant_failovers);
  if (opt_protocol)
  mysql_options(mysql,MYSQL_OPT_PROTOCOL,(char*)&opt_protocol);
  if (opt_plugin_dir && *opt_plugin_dir)
@@ -1805,6 +1808,11 @@ static struct my_option my_long_options[] =
  &opt_mysql_unix_port, &opt_mysql_unix_port, 0, GET_STR_ALLOC,
  REQUIRED_ARG, 0, 0, 0, 0, 0, 0},
 #include "sslopt-longopts.h"
+ {"follow-instant-failovers", 0,
+ "Follow instant failovers. Disable with "
+ "--disable-follow-instant-failovers. This option is enabled by default.",
+ &opt_follow_instant_failovers, &opt_follow_instant_failovers,
+ 0, GET_BOOL, OPT_ARG, 1, 0, 0, 0, 0, 0},
  {"table", 't', "Output in table format.", &output_tables,
  &output_tables, 0, GET_BOOL, NO_ARG, 0, 0, 0, 0, 0, 0},
  {"tee", OPT_TEE,

mysql-test/main/mysqld--help.result

@@ -433,6 +433,20 @@ The following specify which files/extra groups are read (specified before remain
  Set the replication role. One of: MASTER, SLAVE
  --init-slave=name Command(s) that are executed by a slave server each time
  the SQL thread starts
+ --instant-failover-mode=name 
+ Instant failover mode. Possible modes are: OFF - No
+ instant failover, ON: Unconditionally redirect new
+ clients connecting over the network via the standard
+ server port to INSTANT_FAILOVER_TARGET (no redirection of
+ local socket-based connections, nor of connections to the
+ EXTRA_PORT), ALL: Unconditionally redirect all new
+ clients to INSTANT_FAILOVER_TARGET (even via local
+ socket-based connections and the EXTRA_PORT).
+ --instant-failover-target=name 
+ Instant failover target. This should be a hostname, an IP
+ address, or a hostname or IP address followed by ':PORT'.
+ Instant failover will not be activated unless
+ INSTANT_FAILOVER_MODE is also set.
  --interactive-timeout=# 
  The number of seconds the server waits for activity on an
  interactive connection before closing it
@@ -1706,6 +1720,8 @@ init-connect
 init-file (No default value)
 init-rpl-role MASTER
 init-slave 
+instant-failover-mode OFF
+instant-failover-target (No default value)
 interactive-timeout 28800
 join-buffer-size 262144
 join-buffer-space-limit 2097152