The first pod with network latency impact user workloads, however,
it is difficuly to understand where is the problem of this latency,
since it depends on the CNI plugin to be ready at the moment of the
pod creation.
Add a new internal metric in the kubelet that allow developers and cluster
administrator to understand the source of the latency problems on
node startups.
kubelet_first_network_pod_start_sli_duration_seconds
Change-Id: I4cdb55b0df72c96a3a65b78ce2aae404c5195006
