perform policy check before deleting association record
perform policy check before deleting association record

- perform policy check (admins group, in this case) prior to deleting
  the org_user_association record for a user. This prevents a situation
  where the user fails to delete the user record because it is in the
  admin group, but a portion of that deletion actually does occur.
- slight reorganization of user disassociation code to make intentions
  more clear

juliandunn/chef-server-1,stephenbm/chef-server,charlesjohnson/chef-server,juliandunn/chef-server-1,poliva83/chef-server,poliva83/chef-server,chef/chef-server,chef/oc_erchef,itmustbejj/chef-server,vladuemilian/chef-server,juliandunn/chef-server-1,chef/chef-server,charlesjohnson/chef-server,marcparadise/chef-server,charlesjohnson/chef-server,itmustbejj/chef-server,stephenbm/chef-server,stephenbm/chef-server,rmoorman/chef-server,stephenbm/chef-server,Minerapp/chef-server,itmustbejj/chef-server,juliandunn/chef-server-1,chef/chef-server,chef/chef-server,rmoorman/chef-server,chef/oc_erchef,marcparadise/chef-server,itmustbejj/chef-server,vladuemilian/chef-server,chef/oc_chef_wm,charlesjohnson/chef-server,marcparadise/chef-server,Minerapp/chef-server,itmustbejj/chef-server,marcparadise/chef-server,juliandunn/chef-server-1,vladuemilian/chef-server,stephenbm/chef-server,marcparadise/chef-server,rmoorman/chef-server,Minerapp/chef-server,rmoorman/chef-server,rmoorman/chef-server,vladuemilian/chef-server,chef/chef-server,chef/oc_erchef,chef/chef-server,charlesjohnson/chef-server,poliva83/chef-server,vladuemilian/chef-server,chef/oc_erchef,poliva83/chef-server,Minerapp/chef-server,poliva83/chef-server,Minerapp/chef-server