unmanaged kube-dns: Delete one pod per iteration
unmanaged kube-dns: Delete one pod per iteration

Under some circumstances, such as the initial boot up of cilium and
cilium operator in a cluster, the original code would iterate through
all kube-dns pods and delete them in a single pass, causing momentary
clusterwide DNS outage.

With this, a single kube-dns pod will be deleted per iteration.
It is still suboptimal, since it relies on hope and quick coredns
startup, but it is arguably better than taking down the DNS service for
a few seconds.

Signed-off by: Jean Raby <jean@raby.sh>

tgraf/cilium,tklauser/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,tgraf/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,cilium-team/cilium,michi-covalent/cilium,tgraf/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,cilium-team/cilium,tgraf/cilium,cilium/cilium