Parse error in mtr tests when using $rpl_check_server_ids

Task of this MDEV (and related commits) should be:

1. Make rpl_check_server_ids work again.
2. Remove extra connections namely server_[1,2,..]_1, that were created during initalization in rpl_init.inc, recreated in rpl_reconnect.inc and removed in rpl_end.inc.
   They are dead connections, not used anywhere in rpl suite.
3. Cosmetic fixes
   • Fix errors in `rpl_init.inc` regarding the comments
     • sed 's/.cfg/.cnf/'
     • Verifying server_id is not by default but with using rpl_check_server_ids parameter.
     • Add comment why extra connections server_[i,..,N]_1 are needed, since there is no usage of env variables [MASTER,SLAVE]_PORT1 except in rpl_show_slave_hosts.test.
   • Cleanup type,style cleanup

1. For the first part, consider the test case with configuration options
   • Config rpl_anel.cnf

     !include ../my.cnf

   • Test case rpl_anel.test

     --let $rpl_debug= 1

     --let $rpl_check_server_ids= 1

     --source include/master-slave.inc

     SELECT 1;

     # End of tests

     --source include/rpl_end.inc

   • When setting rpl_check_server_ids parsing error is raised

     ---- Check that @@server_id is distinct for all servers ----

     ..==== BEGIN include/assert.inc [Servers 2 and 1 should have different @@server_id] ====

     .. con='server_1' warn='1' qlog='1' rlog='1' aborterr='1'

     # debug: assert_text='Servers 2 and 1 should have different @@server_id' assert_cond=''

     # debug: interpolated_cond=''

     CURRENT_TEST: rpl.rpl_anel

     mysqltest: In included file "./include/assert.inc":

     included from ./include/rpl_init.inc at line 209:

     included from ./include/master-slave.inc at line 39:

     included from /home/anel/GitHub/mariadb/server/src/10.11/mysql-test/suite/rpl/t/rpl_anel.test at line 4:

     At line 148: query 'let $_assert_result= `SELECT $_assert_cond_interp`' failed: ER_PARSE_ERROR (1064): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 1

   • This error is obtained from mysql-test/include/rpl_init.inc file, when invoking ./include/assert.inc.
   • As proof of working feature attach the test file with rpl_debug enabled, since currently result file cannot be saved with rpl_debug that is storing the PORT numbers, that are failing in buildbot.