Fix VyOS check mode (#35977)

* Revert "commented out check tests (#35788)"

This reverts commit 3df2561405.

* `discard_changes()` now uses `exit discard`

instead of just `discard`. Also a slight tweak to avoid a second `exit` after
`exit discard`

lib/ansible/module_utils/network/vyos/vyos.py

@@ -29,7 +29,7 @@ import json
 from ansible.module_utils._text import to_text
 from ansible.module_utils.basic import env_fallback, return_values
 from ansible.module_utils.network.common.utils import to_list
-from ansible.module_utils.connection import Connection
+from ansible.module_utils.connection import Connection, ConnectionError
 
 _DEVICE_CONFIGS = {}
 
@@ -143,14 +143,13 @@ def load_config(module, commands, commit=False, comment=None):
     if commit:
         try:
             out = connection.commit(comment)
-        except:
+        except ConnectionError:
             connection.discard_changes()
             module.fail_json(msg='commit failed: %s' % out)
-
-    if not commit:
-        connection.discard_changes()
+        else:
+            connection.get('exit')
     else:
-        connection.get('exit')
+        connection.discard_changes()
 
     if diff:
         return diff

lib/ansible/plugins/cliconf/vyos.py

@@ -26,7 +26,7 @@ from itertools import chain
 
 from ansible.module_utils._text import to_bytes, to_text
 from ansible.module_utils.network.common.utils import to_list
-from ansible.plugins.cliconf import CliconfBase, enable_mode
+from ansible.plugins.cliconf import CliconfBase
 
 
 class Cliconf(CliconfBase):
@@ -69,7 +69,7 @@ class Cliconf(CliconfBase):
         self.send_command(to_bytes(command))
 
     def discard_changes(self, *args, **kwargs):
-        self.send_command(b'discard')
+        self.send_command(b'exit discard')
 
     def get_capabilities(self):
         result = {}

test/integration/targets/vyos_smoke/tests/cli/misc_tests.yaml

@@ -1,13 +1,13 @@
 # hit check conditional in module_utils.network.vyos -> load_config()
-# - name: configure simple config command
-#   vyos_config:
-#     lines: set system host-name check-test
-#   check_mode: yes
-#
-# - name: get host name
-#   vyos_command:
-#     commands: show host name
-#   register: result
-#
-# - assert:
-#     that: '"check-test" not in result.stdout'
+- name: configure simple config command
+  vyos_config:
+    lines: set system host-name check-test
+  check_mode: yes
+
+- name: get host name
+  vyos_command:
+    commands: show host name
+  register: result
+
+- assert:
+    that: '"check-test" not in result.stdout'