Adds support for Multus (multiple interfaces) CNI plugin (#3166)

* Adds support for Multus (multiple interfaces) CNI plugin

Multus is a latin word for "Multi". As the name suggests, it acts as a
Multi plugin in Kubernetes and provides multiple network interface
support in a pod. Multus uses the concept of invoking delegates by
grouping multiple plugins into delegates and invoking them in the
sequential order of the CNI configuration file provided in json format.

* Change CNI version (0.1.0->0.3.1) of Contiv to be compatible with Multus

.gitlab-ci.yml

@@ -300,6 +300,10 @@ before_script:
 # stage: deploy-special
   MOVED_TO_GROUP_VARS: "true"
 
+.centos7_multus_calico_variables: &centos7_multus_calico_variables
+# stage: deploy-part2
+  MOVED_TO_GROUP_VARS: "true"
+
 .coreos_alpha_weave_ha_variables: &coreos_alpha_weave_ha_variables
 # stage: deploy-special
   MOVED_TO_GROUP_VARS: "true"
@@ -638,6 +642,17 @@ gce_centos7-kube-router:
   except: ['triggers']
   only: ['master', /^pr-.*$/]
 
+gce_centos7-multus-calico:
+  stage: deploy-part2
+  <<: *job
+  <<: *gce
+  variables:
+    <<: *gce_variables
+    <<: *centos7_multus_calico_variables
+  when: manual
+  except: ['triggers']
+  only: ['master', /^pr-.*$/]
+
 gce_opensuse-canal:
   stage: deploy-part2
   <<: *job