containernetworking-cni: Arbitrary path injection via type field in CNI configuration

An improper limitation of path name flaw was found in containernetworking/cni in versions before 0.8.1. When specifying the plugin to load in the 'type' field in the network configuration, it is possible to use special elements such as "../" separators to reference binaries elsewhere on the system. This flaw allows an attacker to execute other existing binaries other than the cni plugins/types, such as 'reboot'. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.