caching: Fix containerd, improve console messages, add integration tests

[tstromberg]

• Change output messages to use "download" instead of "caching", for accuracy and familiarity.
• 'ctr cri load' doesn't work, use 'ctr image import' instead.
• LoadImage errors are no longer fatal, though it still outputs an error message to console.
• TestStartStop now tests caching!
• Allow integration tests to pass arguments directly to Start()

Closes #3651

[k8s-ci-robot]

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[tstromberg]

@minikube-bot OK to test

[afbjorklund]

Why did you need to use sudo for docker ? The default user should be part of the root-equivalent group:

$ ls -l /var/run/docker.sock 
srw-rw---- 1 root docker 0 Feb 28 16:48 /var/run/docker.sock
$ id
uid=1001(docker) gid=1001(docker) groups=1001(docker),10(wheel),1000(rkt),1018(rkt-admin),1019(vboxsf)

$ docker save busybox | gzip > busybox.tar.gz
$ docker load < busybox.tar.gz 
Loaded image: busybox:latest

https://docs.docker.com/install/linux/linux-postinstall/#manage-docker-as-a-non-root-user

[tstromberg]

Why did you need to use sudo for docker ? The default user should be part of the root-equivalent group:

$ ls -l /var/run/docker.sock 
srw-rw---- 1 root docker 0 Feb 28 16:48 /var/run/docker.sock
$ id
uid=1001(docker) gid=1001(docker) groups=1001(docker),10(wheel),1000(rkt),1018(rkt-admin),1019(vboxsf)

$ docker save busybox | gzip > busybox.tar.gz
$ docker load < busybox.tar.gz 
Loaded image: busybox:latest

https://docs.docker.com/install/linux/linux-postinstall/#manage-docker-as-a-non-root-user

You appear to be completely correct. I put that change in a couple of weeks ago and completely forgot why I added sudo. The answer appears to be, for no reason at all. Thanks for questioning it!

[tstromberg]

@minikube-bot OK to test

[tstromberg]

@minikube-bot OK to test

[tstromberg]

@minikube-bot OK to test

[tstromberg]

@minikube-bot OK to test

[tstromberg]

None failure: #3873

[tstromberg]

@minikube-bot OK to test

[balopat]

LGTM