Invalidate assignment cache on modify operations

Fix another race condition in tempest tests that is caused by improper
cache invalidation.

Invalidate assignment cache in _delete_domain_assignments and role
assignments.

Change-Id: I94b1b9a725575735cceac0c470168fa7d2a1f4e9
Signed-off-by: Artem Goncharov <artem.goncharov@gmail.com>

keystone/assignment/core.py

@@ -84,6 +84,7 @@ class Manager(manager.Manager):
     ):
         domain_id = payload['resource_info']
         self.driver.delete_domain_assignments(domain_id)
+        COMPUTED_ASSIGNMENTS_REGION.invalidate()
 
     def _get_group_ids_for_user_id(self, user_id):
         # TODO(morganfainberg): Implement a way to get only group_ids
@@ -1337,6 +1338,7 @@ class Manager(manager.Manager):
         self.driver.create_system_grant(
             role_id, user_id, target_id, assignment_type, inherited
         )
+        COMPUTED_ASSIGNMENTS_REGION.invalidate()
 
     def delete_system_grant_for_user(self, user_id, role_id):
         """Remove a system grant from a user.
@@ -1408,6 +1410,7 @@ class Manager(manager.Manager):
         self.driver.create_system_grant(
             role_id, group_id, target_id, assignment_type, inherited
         )
+        COMPUTED_ASSIGNMENTS_REGION.invalidate()
 
     def delete_system_grant_for_group(self, group_id, role_id):
         """Remove a system grant from a group.