properly set is_system_auditor on initial LDAP login

django-auth-ldap recently changed its behavior at login to *delay* the
user.save() call:

b777321fb4

our current process of discovering and setting up the system auditor
role at LDAP login *relies* on the user having a primary key, so this
code now manually calls .save() to enforce one

awx/main/models/__init__.py

@@ -122,7 +122,11 @@ def user_is_system_auditor(user):
 
 @user_is_system_auditor.setter
 def user_is_system_auditor(user, tf):
-    if user.id:
+    if not user.id:
+        # If the user doesn't have a primary key yet (i.e., this is the *first*
+        # time they've logged in, and we've just created the new User in this
+        # request), we need one to set up the system auditor role
+        user.save()
     if tf:
         role = Role.singleton('system_auditor')
         # must check if member to not duplicate activity stream