MDEV-27775 : Some Galera tests fail on FreeBSD due to "unknown signal 9"

Replace 9 with KILL

mysql-test/suite/galera/include/kill_galera.inc

@@ -16,7 +16,7 @@ if (!$kill_signal)
 --let KILL_NODE_PIDFILE = `SELECT @@pid_file`
 
 --perl
-        my $kill_sig = $ENV{'KILL_SIGNAL_VALUE'}
+        my $kill_sig = $ENV{'KILL_SIGNAL_VALUE'};
         my $pid_filename = $ENV{'KILL_NODE_PIDFILE'};
         my $mysqld_pid = `cat $pid_filename`;
         chomp($mysqld_pid);

mysql-test/suite/galera/r/galera_ist_restart_joiner.result

@@ -16,6 +16,7 @@ SET SESSION wsrep_on=ON;
 connection node_1;
 UPDATE t1 SET f2 = 'd' WHERE f1 > 3;
 connection node_2;
+Killing server ...
 connection node_1;
 UPDATE t1 SET f2 = 'e' WHERE f1 > 4;
 connection node_2;

mysql-test/suite/galera/t/galera_ist_restart_joiner.test

@@ -63,19 +63,7 @@ UPDATE t1 SET f2 = 'd' WHERE f1 > 3;
 
 # Kill node #2 while IST is in progress
 --connection node_2
-
-# Kill the connected server
---disable_reconnect
-
---perl
-        my $pid_filename = $ENV{'KILL_NODE_PIDFILE'};
-        my $mysqld_pid = `cat $pid_filename`;
-        chomp($mysqld_pid);
-        system("kill -9 $mysqld_pid");
-        exit(0);
-EOF
-
---source include/wait_until_disconnected.inc
+--source include/kill_galera.inc
 
 --connection node_1
 --source include/wait_until_connected_again.inc