Add attribute to accept passphrase, when using a private key file.

[KB-perByte]

SUMMARY

Added support for private key passphrase in libssh connection plugin, when using encrypted private keys specified by the C(ansible_private_key_file) attribute.
Set libssh logging level to DEBUG when Ansible verbosity is greater than 3, to aid in troubleshooting connection issues.
Works well with - ansible/pylibssh#597

ISSUE TYPE

• Feature Pull Request

COMPONENT NAME

libssh.py

ADDITIONAL INFORMATION

    ios:
      ansible_connection: network_cli
      ansible_network_os: ios
      ansible_ssh_user: admin
      ansible_ssh_private_key_file: ~/.ssh/test-key-pub
      ansible_private_key_passphrase=mysecretpassphrase
      ansible_become_method: enable
      ansible_network_cli_ssh_type: libssh
      ansible_libssh_config_file: test-key-pub-config