move chef_wm/chef_wm_password to chef_objects/chef_password

* add renamed module and test files.
* move password extraction and conversion to be contained within
  chef_user:new_record and chef_user:update_from_ejson
* expand test converage to include password updates
  and serialized object merge behavior
always used embedded salt for bcrypt-encoded hashes
Merge pull request #72 from opscode/mp/move-password-to-chef-objects

move chef_wm/chef_wm_password to chef_objects/chef_password