infra/common: document guest OS power down command

Add the power off command which was not explicilty mentioned in the
virtualization documentation.
Suggested-by: Rohit Mathew <rohit.mathew@arm.com>
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: I00576901dff6b0b9e37706f0b4e7edb209fa5d4e

docs/infra/common/virtualization.rst

@@ -163,12 +163,18 @@ Launching multiple guests using lkvm:
     309 guest-309            running
     276 guest-276            running
 
-- Power-off the guests by jumping to the right screen, and the guests would
-  shutdown fine with the following log:
+- Power-off the guests by jumping to the right screen and executing the command:
 
-   ::
+  ::
+
+    poweroff
+
+- The guests would shutdown and the following message would be displayed on the
+  console.
+
+  ::
 
-      # KVM session ended normally.
+    # KVM session ended normally.
 
 This completes the procedure to launch multiple VMs and terminate them.
 
@@ -314,12 +320,18 @@ PCI pass-through using multiple guests and smmu test engine:
 
       lkvm debug -a -i stat
 
-- Power-off the guest by jumping to the appropriate screen and the guests would
-  shutdown gracefully with the following log:
+- Power-off the guests by jumping to the right screen and executing the command:
 
-   ::
+  ::
+
+    poweroff
+
+- The guests would shutdown and the following message would be displayed on the
+  console.
+
+  ::
 
-      # KVM session ended normally.
+    # KVM session ended normally.
 
 
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