move chef_wm/chef_wm_password to chef_objects/chef_password

* add renamed module and test files. (chef_wm_password -> chef_password, chef_wm_password_tests -> chef_password_tests) 
* 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

ping @opscode/server-team