Make source jobs voting and gating

As discussed in Kolla IRC meeting 26th July 2018 [1].

[1]
http://eavesdrop.openstack.org/meetings/kolla/2018/kolla.2018-07-25-15.00.log.html#l-77

Change-Id: I6fc46658a9516e44843f31a308504534a6b93d8d

zuul.d/jobs.yaml

@@ -3,7 +3,6 @@
     name: kolla-ansible-centos-source
     parent: kolla-ansible-base
     nodeset: kolla-ansible-centos
-    voting: false
     vars:
       base_distro: centos
       install_type: source
@@ -12,7 +11,6 @@
     name: kolla-ansible-ubuntu-source
     parent: kolla-ansible-base
     nodeset: kolla-ansible-xenial
-    voting: false
     vars:
       base_distro: ubuntu
       install_type: source

zuul.d/project.yaml

@@ -13,6 +13,8 @@
         - openstack-tox-lower-constraints
     gate:
       jobs:
+        - kolla-ansible-centos-source
+        - kolla-ansible-ubuntu-source
         - openstack-tox-lower-constraints
     periodic:
       jobs: