Fix mandatory statement error for junos modules (#50074)

* Fix mandatory statement error for junos modules

Fixes #40267

*  Add error regex in junos terminal plugin to error out
   in case of commit fails

*  If commit fails add logic to discard changes before existing
   else next task will result in error

* Add integration test

* Minor update

test/integration/targets/junos_config/tests/cli_config/cli_basic.yaml

@@ -43,6 +43,17 @@
       - "result.changed == true"
       - "'ge-0/0/2' in result.diff.prepared"
 
+- name: remove root-authethication (test error scenario)
+  cli_config:
+    config: "delete system root-authentication"
+  ignore_errors: True
+  register: result
+
+- assert:
+    that:
+      - "result.failed == true"
+      - "'Missing mandatory statement' in result.msg"
+
 - name: teardown
   cli_config: *rm1