Delay the crash system command

One of the HanaSR test is about crashing one cluster node running HANA.
Crash command is executed through a ssh channel. Problem is that, as soon as the
system crash, the ssh connection  is interrupted leaving the ssh client blocked.
The idea is: compose the remotely executed command with a sleep and then the crash,
run these two in background. It gives time to the ssh client to close the
session before the crash happening.
Remove the timepout=0 behavior, stop forwarding to run_ssh_command all
the args content.

lib/sles4sap_publiccloud.pm

@@ -354,9 +354,14 @@ sub stop_hana {
     $args{method} //= 'stop';
     my $timeout = bmwqemu::scale_timeout($args{timeout} // 300);
     my %commands = (
-        stop => "HDB stop",
-        kill => "HDB kill -x",
-        crash => "echo b > /proc/sysrq-trigger &"
+        stop => 'HDB stop',
+        kill => 'HDB kill -x',
+        # -b is for running the command in background
+        # echo b > /proc/sysrq-trigger is for crashing the remote node
+        # sleep 5 is to give time sudo to put the command execution in background and
+        # to ssh to return, both before to trigger the crash
+        # This also work in conjunction with ssh -fn arguments
+        crash => 'sudo -b sh -c "sleep 5; echo b > /proc/sysrq-trigger"'
     );
     croak("HANA stop method '$args{method}' unknown.") unless $commands{$args{method}};
 
@@ -368,17 +373,40 @@ sub stop_hana {
     record_info("Stopping HANA", "CMD:$cmd");
     if ($args{method} eq "crash") {
         # Crash needs to be executed as root and wait for host reboot
+
+        # Ensure the remote node is in a normal state before to trigger the crash
         $self->{my_instance}->wait_for_ssh(timeout => $timeout);
-        $self->{my_instance}->run_ssh_command(cmd => "sudo su -c sync", timeout => "0", %args);
-        # Try only extending ssh_opts
-        my $ssh_opts = $self->{my_instance}->ssh_opts . ' -o ServerAliveInterval=2';
-        $self->{my_instance}->run_ssh_command(cmd => 'sudo su -c "' . $cmd . '"',
-            timeout => "0",
-            ssh_opts => $ssh_opts,
-            %args);
-        # Send a Ctrl-C to unblock the terminal session if no prompt is seen in 30 seconds
+
+        $self->{my_instance}->run_ssh_command(cmd => "sudo su -c sync", timeout => $timeout);
+
+        # Create a local instance of ssh_opts only for the crash command
+        # it is about extending options defined in sles4sap_publiccloud_basetest::set_cli_ssh_opts
+        # -f requests ssh to go to background just before command execution
+        # -n is about stdin redirection and it is needed by -f to work
+        my $crash_ssh_opts = $self->{my_instance}->ssh_opts . ' -fn -o ServerAliveInterval=2';
+
+        $self->{my_instance}->run_ssh_command(
+            cmd => $cmd,
+            # This timeout is to ensure the run_ssh_command is executed in a reasonable amount of time.
+            # It is not about how much time the crash is expected to take to be executed remotely,
+            # as that one is configured to be executed in background.
+            # So, in theory, run_ssh_command returns immediately, and 10 has nothing to do with the value of sleep 5 executed remotely
+            # Also consider that internally run_ssh_command is using this value for two different guard mechanism.
+            timeout => 10,
+            ssh_opts => $crash_ssh_opts);
+
+
+        # crash trigger command:
+        #  - is executed in background
+        #  - has sleep 5 executed remotely.
+        # run_ssh_command return immediately, so before the remote system execute the crash command.
+        # So the test execution has to sleep now, waiting that remote system has time to execute the crash procedure.
+        sleep 10;
+
+        # Send a Ctrl-C to unblock the terminal session if no prompt is seen here
         type_string('', terminate_with => 'ETX') unless (wait_serial(serial_term_prompt()));
-        # It is better to wait till ssh disappear
+
+        # Wait till ssh disappear
         record_info("Wait ssh disappear start");
         my $out = $self->{my_instance}->wait_for_ssh(timeout => 60, wait_stop => 1);
         record_info("Wait ssh disappear end", "out:" . ($out // 'undefined'));