Update default plugin handling mechanism

[sushanthakumar]

What happened:
Cni Genie supports default plugin selection mechanism as mentioned here
https://github.com/cni-genie/CNI-Genie/blob/master/docs/default-plugin/README.md

So while using genie , when no cni annotations are found and no default plugins are specified, genie will use "weave" as the plugin as a final fallback mechanism
In a case, where genie is installed and some plugin(s) are installed other than weave,
pod with no cni annotaion and no default plugin specification will not be coming to run state as genie will try to use weave in this case which is not installed

What you expected to happen:
In such case (pod no cni annotation/no default plugin) , genie can use the kubelet way of plugin selection ie checking for valid conf file with given order. This will make sure that if any plugin is installed, pod will always be able to get ip address

How to reproduce it (as minimally and precisely as possible):
Create cluster
Install Genie first and then install any non weave plugin
Create a pod with normal yaml (without any genie specific configs)

Anything else we need to know?: -NA-