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

@@ -353,9 +353,9 @@ 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',
+        crash => 'sudo -b  sh -c "sleep 5; echo b > /proc/sysrq-trigger"''
     );
     croak("HANA stop method '$args{method}' unknown.") unless $commands{$args{method}};
 
@@ -368,14 +368,24 @@ sub stop_hana {
     if ($args{method} eq "crash") {
         # Crash needs to be executed as root and wait for host reboot
         $self->{my_instance}->wait_for_ssh(timeout => $timeout);
-        $self->{my_instance}->run_ssh_command(cmd => "sudo su -c sync", timeout => "0", %args);
-        # Close SSH mux file before Crash test
-        $self->{my_instance}->run_ssh_command(cmd => " ", timeout => "0", ssh_opts => "-O exit");
-        $self->{my_instance}->run_ssh_command(cmd => 'sudo su -c "' . $cmd . '"',
-            timeout => "0",
-            # Try only extending ssh_opts
-            ssh_opts => "-o ServerAliveInterval=2 -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -o LogLevel=ERROR",
-            %args);
+        $self->{my_instance}->run_ssh_command(cmd => "sudo su -c sync", timeout => $timeout);
+        $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 executed remotely, as that one is
+            # configured to be executed in background.
+            # So, in theory, the run_ssh_command is expected to immediately return.
+            # Also consider that internally run_ssh_command is using this value for
+            # two different guard mechanism.
+            timeout => 10,
+            # Try only extending ssh_opts. -fn is needed to be able to detachleaving crash to run in background
+            ssh_opts => "-fn -o ServerAliveInterval=2 -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -o LogLevel=DEBUG3");
+
+        # crash has sleep 5 executed remotely. As it also has & to put in background,
+        # run_ssh_command return immediately, so even before the remote system execute the crash command
+        # So now sleep to wait that remote system has time to execute the crash procedure.
+        sleep 50;
+
         # It is better to wait till ssh disappear
         record_info("Wait ssh disappear start");
         my $out = $self->{my_instance}->wait_for_ssh(timeout => 60, wait_stop => 1);