KNIFE-478: Add ability to bootstrap with SSH passwords

[jmccann]

Pass to knife bootstrap the SSH password either specified from command
line or from openstack server instance.

Added tests to make sure it works.

This is to address https://tickets.opscode.com/browse/KNIFE-478

[adamedx]

Looks good, thank you for the tests as well @jmccann.

[siddheshwar-more]

@jmccann
We have same change for openstack knife-cloud:
Branch ref: https://github.com/opscode/knife-openstack/tree/sid-bootstrap-with-ssh-password

Can you please test this at your end? We can't test this with our openstack setup.

here's possible scenarios:
1>With no --ssh-password, it will take from openstack server instance(i.e server.password)
Ex: bundle exec knife openstack server create -N testserver1 -f <"flavor_id"> -I <"image_id"> -c <"knife_rb_file_path"> --ssh-user <"user_name"> --image-os-type linux -VV
2> With --ssh-user <"user_name"> --ssh-password <"password">, it should use user provided password for bootstrap
3> With --ssh-user <"user_name"> --openstack-ssh-key-id <"ssh_key_id"> --identity-file <"openstack_keypair_filepath">

Thank You!!!