WIP: winbindd: handle "NT Authority"

Without this:

  $ bin/wbinfo -n "NT Authority/Authenticated Users"
  failed to call wbcLookupName: WBC_ERR_DOMAIN_NOT_FOUND
  Could not lookup name NT Authority/Authenticated Users

  $ bin/wbinfo --group-info="NT Authority/Authenticated Users"
  failed to call wbcGetgrnam: WBC_ERR_DOMAIN_NOT_FOUND
  Could not get info for group NT Authority/Authenticated Users

With the patch:

  $ bin/wbinfo -n "NT Authority/Authenticated Users"
  S-1-5-11 SID_WKN_GROUP (5)

  $ bin/wbinfo --group-info="NT Authority/Authenticated Users"
  NT AUTHORITY\authenticated users:x:10002:
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