Specify the networks to be used per pod

Specify the networks to be used per pod

If CRD "Network" is defined and network items are created, each pod (server)
can have access to one or several networks. This is defined in the metadata
section, as "annotations.networks" [1].

Example of Kubernetes pod definition with networks:
  apiVersion: v1
  kind: Pod
  metadata:
    name: test-pod
    annotations:
      networks: '[{"name": "flannel"}]'

Example of Yardstick server definition with networks:
  context:
    type: Kubernetes
    servers:
      host:
        containers:
          - name: ...
        networks:
          - flannel  # These names must be defined in
                     # context.networks
    ...
    networks:
      - name: flannel
        plugin: flannel

Kubernetes annotations [2].

[1]https://github.com/intel/multus-cni/tree/b9446232cdf4f1b6f2bea583291973cc97e963f4#configuring-multus-to-use-kubeconfig-and-a-default-network
[2]https://kubernetes.io/docs/concepts/overview/working-with-objects/annotations/

JIRA: YARDSTICK-1178

Change-Id: I6e7b4bacf10810833ec733c14d44e5db613675e3
Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>