Allow ssh agent usage for junos_netconf

By default the `Shell` class disables ssh agents. The `junos_netconf`
module uses this class, but doesn't re-enable agents.
Here it's explicitly enabled again, so an ssh agent can be used to
connect to and configure Junos devices.

lib/ansible/module_utils/junos.py

@@ -95,7 +95,7 @@ class Cli(object):
 
         try:
             self.shell = Shell()
-            self.shell.open(host, port=port, username=username, password=password, key_filename=key_filename)
+            self.shell.open(host, port=port, username=username, password=password, key_filename=key_filename, allow_agent=True)
         except ShellError:
             e = get_exception()
             msg = 'failed to connect to %s:%s - %s' % (host, port, str(e))