Update stack doesn't pause with pre-update hook set

Steps to reproduce:
1. Go to Project -> Orchestration panel
2. Click launch a stack
3. Enter the following in template source
heat_template_version: 2015-04-30
resources:
  test_resource_pause:
     type: OS::Heat::TestResource
     properties:
       action_wait_secs: {"delete": 5, "create": 5, "update": 5}
       client_name: openstack
4. Enter the following in environment source
resource_registry:
  resources:
     test_resource_pause:
        type: OS::Heat::TestResource
        hooks: pre-update
5. Enter other stack information
6. After the stack is created, click on update stack template
7. Enter the template and environment source as in step 3 and 4 and click update stack
8. The stack was updated successfully right away

Expect the update action will stay in progress until the pre-update hook is cleared.

This issue appears to be a heat defect but it's actually caused by horizon not passing the environment data to the heat api.