test: Check kubectl with 'which' instead of 'dpkg -l'
test: Check kubectl with 'which' instead of 'dpkg -l'

When k8s install falls back to binary install kubelet does not exist
as a package, but exists in the path. Use 'which kubelet' to check k8s
install instead of 'dpkg -l' to cover both install methods.

This change fixes the failure to run ginkgo again on an already
running set of k8s nodes when k8s has been installed as binaries.

Signed-off-by: Jarno Rajahalme <0f1ab0ac7dffd9db21aa539af2fd4bb04abc3ad4@covalent.io>
tgraf/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,cilium-team/cilium,michi-covalent/cilium,tklauser/cilium,tgraf/cilium,tklauser/cilium,tklauser/cilium,cilium/cilium,tgraf/cilium,tgraf/cilium,tgraf/cilium,michi-covalent/cilium,cilium-team/cilium,tgraf/cilium,michi-covalent/cilium,tklauser/cilium,tklauser/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium