Add Zuul v3 native midonet cross test

Migrate over legacy-cross-networking-midonet-python35 and convert it to
Zuul v3 native.

Allow .zuul.yaml to be edited, update .gitignore for this.

Change-Id: Icdf5bf8a4a023d4d7a3c12dda3a47cfe4b83b8f3
Needed-By: Ie1040995a66ad7df43b0be48d0ca01e358d06ad4

.gitignore

@@ -30,6 +30,7 @@ subunit.log
 !/.mailmap
 !/.pylintrc
 !/.testr.conf
+!/.zuul.yaml
 
 # Files created by releasenotes build
 releasenotes/build

.zuul.yaml

@@ -0,0 +1,22 @@
+- project:
+    check:
+      jobs:
+        - neutron-fwaas-networking-midonet-cross-py35:
+            voting: false
+
+- job:
+    name: neutron-fwaas-networking-midonet-cross-py35
+    parent: openstack-tox-py35
+    description: |
+      Run Python 35 tests on networking-midonet repository.
+    vars:
+      zuul_work_dir: src/git.openstack.org/openstack/networking-midonet
+    required-projects:
+      - openstack/requirements
+      - openstack/networking-midonet
+      - openstack/neutron
+      - openstack/neutron-vpnaas
+      - openstack/neutron-lbaas
+      - openstack/neutron-dynamic-routing
+      - openstack/networking-l2gw
+      - openstack/tap-as-a-service