node: make node service PartOf=openvswitch.service when openshift-sdn is used

Commit 7f805f9a0c41477365dd88b0ac73f0d221bd654a causes the behavior seen in
https://bugzilla.redhat.com/show_bug.cgi?id=1453113 because openshift-node
is no longer restarted when openvswitch is, due to the change from Requires
to Wants.

Turns out that making the openshift node service PartOf the OVS service
can achieve the same result and ensure openshift-node gets restarted whenever
OVS does, which ensures that networking doesn't break underneath the node.

Suggested by Giuseppe Scrivano

roles/openshift_node/templates/openshift.docker.node.service

@@ -6,6 +6,7 @@ PartOf={{ openshift.docker.service_name }}.service
 Requires={{ openshift.docker.service_name }}.service
 {% if openshift_node_use_openshift_sdn %}
 Wants=openvswitch.service
+PartOf=openvswitch.service
 After=ovsdb-server.service
 After=ovs-vswitchd.service
 {% endif %}

roles/openshift_node_upgrade/templates/openshift.docker.node.service

@@ -6,6 +6,7 @@ PartOf={{ openshift.docker.service_name }}.service
 Requires={{ openshift.docker.service_name }}.service
 {% if openshift_use_openshift_sdn %}
 Wants=openvswitch.service
+PartOf=openvswitch.service
 After=ovsdb-server.service
 After=ovs-vswitchd.service
 {% endif %}