Fix disable_gateway_ip for subnet

When creating a subnet with disable_gateway_ip, the value
was not passed into the creation which would lead into
a subnet being created with a gateway, and then on updates
it would have the gateway removed.

Change-Id: I816d4a4d09b2116c00cf868a590bd92dac4bfc5b

ci/roles/subnet/tasks/main.yml

@@ -142,6 +142,41 @@
   assert:
     that: subnet is not changed
 
+- name: Create subnet {{ subnet_name }} on network {{ network_name }} without gateway IP
+  openstack.cloud.subnet:
+    cloud: "{{ cloud }}"
+    network_name: "{{ network_name }}"
+    name: "{{ subnet_name }}"
+    state: present
+    cidr: 192.168.0.0/24
+    disable_gateway_ip: true
+  register: subnet
+
+- name: Assert changed
+  assert:
+    that: subnet is changed
+
+- name: Create subnet {{ subnet_name }} on network {{ network_name }} without gateway IP
+  openstack.cloud.subnet:
+    cloud: "{{ cloud }}"
+    network_name: "{{ network_name }}"
+    name: "{{ subnet_name }}"
+    state: present
+    cidr: 192.168.0.0/24
+    disable_gateway_ip: true
+  register: subnet
+
+- name: Assert not changed
+  assert:
+    that: subnet is not changed
+
+- name: Delete subnet {{ subnet_name }} again
+  openstack.cloud.subnet:
+    cloud: "{{ cloud }}"
+    name: "{{ subnet_name }}"
+    state: absent
+  register: subnet
+
 - name: Delete network {{ network_name }}
   openstack.cloud.network:
     cloud: "{{ cloud }}"

plugins/modules/subnet.py

@@ -382,6 +382,8 @@ class SubnetModule(OpenStackModule):
             params['allocation_pools'] = self.params['allocation_pools']
         params = self._add_extra_attrs(params)
         params = {k: v for k, v in params.items() if v is not None}
+        if self.params['disable_gateway_ip']:
+            params['gateway_ip'] = None
         return params
 
     def _build_updates(self, subnet, params):