Add ssh_keyfile as an optional argument. (#145)

* Add ssh_keyfile as an optional argument. Also change optional_args to default to an empty dict{}

* Switch back to optional_args=None.

* Add port=self.port and change ssh_keyfile to keyfile to keep it consistent.

* Fix line too long.

napalm_junos/junos.py

@@ -61,8 +61,9 @@ def __init__(self, hostname, username, password, timeout=60, optional_args=None)
         Initialise JunOS driver.
 
         Optional args:
-            * port (int): custom port
             * config_lock (True/False): lock configuration DB after the connection is established.
+            * port (int): custom port
+            * key_file (string): SSH key file path
         """
         self.hostname = hostname
         self.username = username
@@ -71,12 +72,21 @@ def __init__(self, hostname, username, password, timeout=60, optional_args=None)
         self.config_replace = False
         self.locked = False
 
+        # Get optional arguments
         if optional_args is None:
             optional_args = {}
-        self.port = optional_args.get('port', 22)
+
         self.config_lock = optional_args.get('config_lock', True)
+        self.port = optional_args.get('port', 22)
+        self.key_file = optional_args.get('key_file', None)
 
-        self.device = Device(hostname, user=username, password=password, port=self.port)
+        if self.key_file:
+            self.device = Device(hostname,
+                                 user=username,
+                                 ssh_private_key_file=self.key_file,
+                                 port=self.port)
+        else:
+            self.device = Device(hostname, user=username, password=password, port=self.port)
 
         self.profile = ["junos"]