Add psmisc package, for pstree command

[afbjorklund]

I miss my pstree, from the boot2docker machine image...

systemd-+-12*[conmon-+-pause---3*[{pause}]]
        |            `-{conmon}]
        |-conmon-+-kube-scheduler---6*[{kube-scheduler}]
        |        `-{conmon}
        |-conmon-+-kube-addons.sh---sleep
        |        `-{conmon}
        |-conmon-+-kube-apiserver---8*[{kube-apiserver}]
        |        `-{conmon}
        |-conmon-+-etcd---9*[{etcd}]
        |        `-{conmon}
        |-conmon-+-kube-controller---7*[{kube-controller}]
        |        `-{conmon}
        |-conmon-+-coredns---11*[{coredns}]
        |        `-{conmon}
        |-conmon-+-heapster---6*[{heapster}]
        |        `-{conmon}
        |-conmon-+-dnsmasq-nanny-+-dnsmasq
        |        |               `-6*[{dnsmasq-nanny}]
        |        `-{conmon}
        |-conmon-+-sidecar---6*[{sidecar}]
        |        `-{conmon}
        |-conmon-+-influxd---8*[{influxd}]
        |        `-{conmon}
        |-conmon-+-grafana-server-+-setup_grafana
        |        |                `-8*[{grafana-server}]
        |        `-{conmon}
        |-conmon-+-kube-proxy---6*[{kube-proxy}]
        |        `-{conmon}
        |-conmon-+-storage-provisi---6*[{storage-provisi}]
        |        `-{conmon}
        |-conmon-+-kube-dns---7*[{kube-dns}]
        |        `-{conmon}
        |-conmon-+-dashboard---6*[{dashboard}]
        |        `-{conmon}
        |-containerd---11*[{containerd}]
        |-crio---17*[{crio}]
        |-dbus-daemon
        |-dockerd-+-docker-containe---8*[{docker-containe}]
        |         `-8*[{dockerd}]
        |-2*[getty]
        |-kubelet---14*[{kubelet}]
        |-rkt---7*[{rkt}]
        |-rkt---6*[{rkt}]
        |-rpc.mountd
        |-rpc.statd
        |-rpcbind
        |-sshd---sshd---sshd---bash---pstree
        |-systemd-journal
        |-systemd-logind
        |-systemd-network
        |-systemd-resolve
        |-systemd-timesyn---{systemd-timesyn}
        `-systemd-udevd

Makes it easy to e.g. see that dockerd and rkt are still running.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: afbjorklund
To fully approve this pull request, please assign additional approvers.
We suggest the following additional approver: balopat

If they are not already assigned, you can assign the PR to them by writing /assign @balopat in a comment when ready.

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[afbjorklund]

For reference, here was the boring old process tree: (no systemd, no kubeadm, no crio, etc etc)

init-+-acpid
     |-crond
     |-dockerd---docker-containe-+-4*[docker-containe---pause]
     |                           |-docker-containe---kube-addons.sh---sleep
     |                           |-docker-containe---dashboard
     |                           |-docker-containe---kube-dns
     |                           |-docker-containe---storage-provisi
     |                           |-docker-containe---dnsmasq-nanny---dnsmasq
     |                           `-docker-containe---sidecar
     |-forgiving-getty---getty
     |-3*[forgiving-getty---sleep]
     |-localkube
     |-ntpd
     |-sh
     |-sshd-+-sshd---sshd
     |      `-sshd---sshd---sh---pstree
     |-udevd---2*[udevd]
     `-udhcpc

https://github.com/afbjorklund/docker-machine-minikube-install (now deprecated, after v1.10.0)