fixes issue where junos shared module was ignoring ssh_keyfile (#17712)

This fixes a problem with the Netconf transport in which the ssh keyfile
wasn't being used if it was defined.  The ref issue is filed against 2.1.1
but have been unable to replicate the problem in that version

ref: ansible/ansible-modules-core#4966

lib/ansible/module_utils/junos.py

@@ -23,6 +23,7 @@ from distutils.version import LooseVersion
 
 from ansible.module_utils.pycompat24 import get_exception
 from ansible.module_utils.network import register_transport, to_list
+from ansible.module_utils.network import NetworkError
 from ansible.module_utils.shell import CliBase
 from ansible.module_utils.six import string_types
 
@@ -93,14 +94,22 @@ class Netconf(object):
 
     def connect(self, params, **kwargs):
         host = params['host']
-        port = params.get('port') or 830
 
-        user = params['username']
-        passwd = params['password']
+        kwargs = dict()
+        kwargs['port'] = params.get('port') or 830
+
+        kwargs['user'] = params['username']
+
+        if params['password']:
+            kwargs['passwd'] = params['password']
+
+        if params['ssh_keyfile']:
+            kwargs['ssh_private_key_file'] = params['ssh_keyfile']
+
+        kwargs['gather_facts'] = False
 
         try:
-            self.device = Device(host, user=user, passwd=passwd, port=port,
-                                 gather_facts=False)
+            self.device = Device(host, **kwargs)
             self.device.open()
         except ConnectError:
             exc = get_exception()