adds feature to try to auto determine network_os (#18674)

This updates the network_cli connection plugin to attempt to automatically
determine the remote device os.  The device network os discovery can
be overridden by setting the ansible_network_os value.

lib/ansible/plugins/terminal/junos.py

@@ -45,3 +45,9 @@ class TerminalModule(TerminalBase):
         except AnsibleConnectionFailure:
             raise AnsibleConnectionFailure('unable to set terminal parameters')
 
+    @staticmethod
+    def guess_network_os(conn):
+        stdin, stdout, stderr = conn.exec_command('show version')
+        if 'Junos' in stdout.read():
+            return 'junos'
+