Adding support for ssh private key file to fetch remote host hardware information

[skvenkat]

The current approach of fetching hardware info for remote host only uses password authentication mode in paramiko client. In addition to that, supporting the usage of ssh private key to login remote host to fetch info would be more ideal in the case of cloud bases instances.

It can be achieved through the following ways:

1. add another option [-k KEYFILE] to get the private key file as separate input
2. Adding a conditional logic to distinguish the input for password ** @(it should be either password or private key file with absolute path)** and call the client method with appropriate keyword arguments.

This is a good to have feature would help lot to DevOps people.

@rdobson Thanks in advance.