clarified some steps in release instructions

adding priyawadhwa and tstromberg as maintainers

First try "kubeadm reset" without -f, primarily for older versions.

Extend Jenkins integration test timeout from 30m to 50m.

We've recently added TestFunctionalContainerd, which can take 10-15
minutes, pushing us over the edge in many cases.

For newer versions, it seems more pleasant anyways. This approach is at
least less ugly than parsing JSON from a shell script to version sniff.

* Save old cluster config in memory before overwriting

In PR #3426, I changed "minikube start" to overwrite the cluster config earlier so that the container runtime could be extracted from it by the buildroot provisioner. This introduced a bug later on, where minikube expected to read the kubernetes version from theold config (which no longer existed, because the config was overwritten).

To fix this, I changed the code to store the old version of the config in memory before overwriting it.

This should fix #3447

* Change restart policy on gvisor pod

Change the restart policy on the gvisor pod to Always. This way, if a
user runs

minikube addons enable gvisor
minikube stop
minikube start

when the addon manager tries to restart the gvisor pod, it will be
restarted and gvisor will start running automatically. This PR also adds an
integration test for this functionality.

* Test stop and start

* Revert test to delete

Revert test to delete for now, for some reason "stop" and then "start"
is failing both locally and in Jenkins for VirtualBox with a "panic test
timed out after 30 min" error

Fix .Info() error message

* upping the Makefile version
* release notes for 0.31.0

This PR adds the code for enabling gvisor in minikube. It adds the pod
that will run when the addon is enabled, and the code for the image
which will run when this happens.

When gvisor is enabled, the pod will download runsc and the
gvisor-containerd-shim. It will replace the containerd config.toml and
restart containerd.

When gvisor is disabled, the pod will be deleted by the addon manager.
This will trigger a pre-stop hook which will revert the config.toml to
it's original state and restart containerd.

Add apiserver check to "status", and block "start" until it's healthy.

* Only restart docker service if container runtime is docker

Only allow the buildroot provisioner to restart docker if the container
runtime is docker. This change should fix the bug in #3424, since now
docker will not be restarted if the container runtime is containerd.

* Added files to fix FileContent--proc-sys-net-bridge-bridge-nf-call-iptables precheck error

From this issue: https://github.com/kubernetes/kubeadm/issues/1062
these files need to be added to prevent this precheck error (which occurs when running any container runtime that isn't docker).

Also, save the machine config on the user's filesystem earlier so that the buildprovisioner can access it.

Signed-off-by: NJoeWrightss <zhoulin.xie@daocloud.io>

Add schedutils to the guest VM for the ionice command (used by k8s 1.12)

Revert "Make k8s v1.12.3 the default"

Report and clean up stale tunnel routes

kill hung test commands and improve hung process output

This reverts commit fc5256b2.

Make k8s v1.12.3 the default

none cleanup: force kubeadm, clear /etc/kubernetes, and use sudo for kubectl kill