Bug #28780 report_host is not available through SELECT @@report_host

There was no way to see if report-{host,port,user,password} were set up.

Fixed with introducing new global variables.
The variables are made read-only because of a possible need to change them
most probably require the slave server restart.

Todo: transform the startup options to be CHANGE master parameters - i.e
to deprecate `report-' options, and to change the new vars 
to be updatable at time of CHANGE master executes with new
values.

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

+stop slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+reset master;
+reset slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+start slave;
+select * from Information_schema.GLOBAL_VARIABLES where variable_name regexp 'report_\(host\|port\|user\|password\)';
+VARIABLE_NAME	VARIABLE_VALUE
+REPORT_HOST	127.0.0.1
+REPORT_PORT	9308
+REPORT_PASSWORD	my_password
+REPORT_USER	my_user
+show global variables like 'report_host';
+Variable_name	Value
+report_host	127.0.0.1
+show global variables like 'report_port';
+Variable_name	Value
+report_port	9308
+show global variables like 'report_user';
+Variable_name	Value
+report_user	my_user
+show global variables like 'report_password';
+Variable_name	Value
+report_password	my_password
+set @@global.report_host='my.new.address.net';
+ERROR HY000: Variable 'report_host' is a read only variable
+end of tests

mysql-test/suite/rpl/t/rpl_report-slave.opt

+--report-host=127.0.0.1 --report-user='my_user' --report-password='my_password' --report-port=9308
+

mysql-test/suite/rpl/t/rpl_report.test

+# Verify that mysqld init time --report-{host,port,user,password} parameters
+# are SHOW-able and SELECT-able FROM INFORMATION_SCHEMA.global_variables
+
+source include/master-slave.inc;
+
+connection slave;
+select * from Information_schema.GLOBAL_VARIABLES where variable_name regexp 'report_\(host\|port\|user\|password\)';
+show global variables like 'report_host';
+show global variables like 'report_port';
+show global variables like 'report_user';
+show global variables like 'report_password';
+
+# to demonstrate that report global variables are read-only
+error ER_INCORRECT_GLOBAL_LOCAL_VAR;
+set @@global.report_host='my.new.address.net';
+
+
+--echo end of tests

sql/set_var.cc

@@ -648,6 +648,19 @@ sys_var_thd_time_zone            sys_time_zone(&vars, "time_zone");
 
 /* Global read-only variable containing hostname */
 static sys_var_const_str        sys_hostname(&vars, "hostname", glob_hostname);
+static sys_var_const_str_ptr    sys_repl_report_host(&vars, "report_host", &report_host);
+static sys_var_const_str_ptr    sys_repl_report_user(&vars, "report_user", &report_user);
+static sys_var_const_str_ptr    sys_repl_report_password(&vars, "report_password", &report_password);
+
+static uchar *slave_get_report_port(THD *thd)
+{
+  thd->sys_var_tmp.long_value= report_port;
+  return (uchar*) &thd->sys_var_tmp.long_value;
+}
+
+static sys_var_readonly    sys_repl_report_port(&vars, "report_port", OPT_GLOBAL, SHOW_INT, slave_get_report_port);
+
+
 
 sys_var_thd_bool  sys_keep_files_on_create(&vars, "keep_files_on_create", 
                                            &SV::keep_files_on_create);