new blueprint to support user-define password

[Sam Su]

Hi,

In the current Openstack-<some parts name> implementation, all of Openstack services passwords are set as its related service name, I create the blueprint to support user-define password.
https://blueprints.launchpad.net/openstack-chef/+spec/user-define-password-support

I also has an implementation for the BP:
https://review.openstack.org/#/c/97948/1/libraries/passwords.rb

If any concern or suggestion for the BP or implementation, please feel free to comment.

Thanks,
Sam