verify_os_update - mark node dirty after OS update (#4509)

Author: SRIKKANTH

lisa/microsoft/testsuites/core/azure_image_standard.py

@@ -719,10 +719,18 @@ def verify_yum_conf(self, node: Node) -> None:
     )
     def verify_os_update(self, node: Node) -> None:
         if isinstance(node.os, Posix):
-            node.os.update_packages("")
+            # After OS update sometimes kernel version may change.
+            # When LISA is used to validate a VM image with specific kernel version,
+            # changing the kernel will result in running tests with undesired kernel
+            # which is not expected.
+            # Marking the node dirty after OS update to avoid such issues.
+            try:
+                node.os.update_packages("")
+            finally:
+                node.mark_dirty()
+            node.reboot()
         else:
             raise SkippedException(f"Unsupported OS or distro type : {type(node.os)}")
-        node.reboot()
 
     @TestCaseMetadata(
         description="""