Added fix to handle mode telnet

[chidanandpujar]

What does this PR do?

To handle mode= telnet and port = 23

isinstance(dev, Device): returns False for device handle with mode=telnet and port=23, added another check to if dev is not None and proceed with execution

What issues does this PR fix or reference?

Ansible issue https://github.com/Juniper/ansible-junos-stdlib/issues/535

Previous Behavior

Remove this section if not relevant "msg": "Uncaught exception - please report: not all arguments converted during string formatting"

Tests written?

Yes/No Need update in inventory local_connection_testcases ansible_host=x.x.x.x ansible_user=xyz ansible_pass=xyz ansible_port=23 mode=telnet ansible_connection=local ansible_command_timeout=300