pkg/asset/internal: standardize around k8s-app label
pkg/asset/internal: standardize around k8s-app label

ericchiang/bootkube,diegs/bootkube,diegs/bootkube,ericchiang/bootkube,diegs/bootkube,kubernetes-incubator/bootkube,kubernetes-incubator/bootkube,hongchaodeng/bootkube,hongchaodeng/bootkube,dghubble/bootkube,ericchiang/bootkube,dghubble/bootkube,kubernetes-incubator/bootkube,dghubble/bootkube,hongchaodeng/bootkube