Update KubeException to inherit StandardError
Update KubeException to inherit StandardError

Currently, KubeException inherits from Exception, which is bad because
the default "rescue" behaviour is to catch only exception which are
StandardException.

everalbum/kubeclient,dkorn/kubeclient,zendesk/kubeclient,moolitayer/kubeclient,zakiva/kubeclient,fabiokr/kubeclient,abonas/kubeclient