Windows_ad_join resource was broken for cross domain authentication

Description

If the "domain_user" 's domain differs from the the domain it is joining this resource will fail. Before #7906 you could pass the domain\user. Now the command expects user and appends the domain to the powershell command.

This is an issue for larger companies with multiple domains.

Chef Version

Chef_version >= 14.8.12

Platform Version

Windows

Replication Case

For domain_user pass a user "domain"\user with a differing "domain" then the domain the machine is joining.

Example

   windows_ad_join <domain_A> do
    domain_password      join_pass
    domain_user          domain_B\maier
    ou_path              join_oupath
    reboot               :delayed
    sensitive            false
   end

Client Output

Failed to join the domain <OUR_DOMAIN>: Add-Computer : Computer '<hostname>' failed to join domain '<OUR_DOMAIN>' from its 
current workgroup 'WORKGROUP' with following error message: The user name or password is 
incorrect.
At line:1 char:181
+ ... com",$pswd);Add-Computer -DomainName <OUR_DOMAIN> -Cred ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : OperationStopped: (<hostname>:String) [Add-Computer], InvalidOpera 
   tionException
    + FullyQualifiedErrorId : FailToJoinDomainFromWorkgroup,Microsoft.PowerShell.Commands.AddComp 
   uterCommand

Stacktrace

C:/opscode/chef/embedded/lib/ruby/gems/2.5.0/gems/chef-14.10.9-universal-mingw32/lib/chef/resource/windows_ad_join.rb:80:in `block (2 levels) in <class:WindowsAdJoin>'
C:/opscode/chef/embedded/lib/ruby/gems/2.5.0/gems/chef-14.10.9-universal-mingw32/lib/chef/mixin/why_run.rb:51:in `add_action'
C:/opscode/chef/embedded/lib/ruby/gems/2.5.0/gems/chef-14.10.9-universal-mingw32/lib/chef/provider.rb:227:in `converge_by'
C:/opscode/chef/embedded/lib/ruby/gems/2.5.0/gems/chef-14.10.9-universal-mingw32/lib/chef/resource/windows_ad_join.rb:74:in `block in <class:WindowsAdJoin>'
(eval):2:in `block in action_join'
C:/opscode/chef/embedded/lib/ruby/gems/2.5.0/gems/chef-14.10.9-universal-mingw32/lib/chef/provider.rb:236:in `instance_eval'
C:/opscode/chef/embedded/lib/ruby/gems/2.5.0/gems/chef-14.10.9-universal-mingw32/lib/chef/provider.rb:236:in `compile_and_converge_action'
(eval):2:in `action_join'
C:/opscode/chef/embedded/lib/ruby/gems/2.5.0/gems/chef-14.10.9-universal-mingw32/lib/chef/provider.rb:182:in `run_action'
C:/opscode/chef/embedded/lib/ruby/gems/2.5.0/gems/chef-14.10.9-universal-mingw32/lib/chef/resource.rb:578:in `run_action'

Start with chef/resource/windows_ad_join.rb around lines 74-80, where the join action builds the PowerShell Add-Computer command. Reproduce the case with domain_user set to a qualified user from a different domain, then verify that the explicitly qualified account is preserved while joining the target domain.