Fix junos modules check_mode issue (#37311)

Fixes #37208

If check_mode is enabled instead of committing th config need to
discard all the chnages to cnadidate db
In case of cli to discard changes issue `rollback 0` command
and for netconf execute `discard-changes` rpc call

lib/ansible/module_utils/network/junos/junos.py

@@ -180,9 +180,9 @@ def locked_config(module):
         unlock_configuration(module)
 
 
-def discard_changes(module, exit=False):
+def discard_changes(module):
     conn = get_connection(module)
-    return conn.discard_changes(exit=exit)
+    return conn.discard_changes()
 
 
 def get_diff(module, rollback='0'):

lib/ansible/plugins/cliconf/junos.py

@@ -84,10 +84,8 @@ class Cliconf(CliconfBase):
         command += b' and-quit'
         return self.send_command(command)
 
-    def discard_changes(self, rollback_id=None):
-        command = b'rollback'
-        if rollback_id is not None:
-            command += b' %s' % int(rollback_id)
+    def discard_changes(self):
+        command = b'rollback 0'
         for cmd in chain(to_list(command), b'exit'):
             self.send_command(cmd)
 

test/integration/targets/junos_banner/tests/netconf/basic.yaml

@@ -78,6 +78,20 @@
       - "result.changed == true"
       - "'<message>this is my login banner</message>' in config.xml"
 
+- name: check mode
+  junos_banner:
+    banner: login
+    text: this is not the login banner you're looking for
+    state: present
+    provider: "{{ netconf }}"
+  register: result
+  check_mode: yes
+
+- assert:
+    that:
+      - "result.changed == true"
+      - "result.failed == false"
+
 - name: delete login banner
   junos_banner:
     banner: login