Comment 0 for bug 1510800

1. create a stack with neutron subnet
***********************
heat_template_version: 2014-10-16
resources:
  subnet:
    type: OS::Neutron::Subnet
    properties:
      network: 3447dd80-14ef-4059-8ea6-35f4fd60ba26
      cidr: 20.0.1.0/29
      gateway_ip: 20.0.1.5

2. want to disassociate the gateway ip(20.0.1.5), so to update the stack with template:
****************************
heat_template_version: 2014-10-16
resources:
  subnet:
    type: OS::Neutron::Subnet
    properties:
      network: 3447dd80-14ef-4059-8ea6-35f4fd60ba26
      cidr: 20.0.1.0/29

3. the stack went to UPDATE_COMPLEATE, but we can find that the subnet also has the gateway ip(20.0.1.5)