toolbox depends on running Docker daemon

[GreatSUN]

Issue Report

When trying to use toolbox on our Kubernetes clusters running on rkt, we see that we would either have to run the Docker daemon or to setup the Containers our self.

As discussed with @euank

Bug

Toolbox should not be depending on a running Docker daemon, instead it would be nicer if Toolbox would make use of rkt which basically doesn't require anything.

CoreOS Version

ALL

BUG_REPORT_URL="https://github.com/coreos/bugs/issues"

Environment

Kubernetes 1,4.6
rkt 1.21.0

What hardware/cloud provider/hypervisor is being used to run CoreOS?
Bare metal

Expected Behavior

Toolbox is not depending on running Docker daemon

Actual Behavior

Toolbox is only working when Docker is enabled

Reproduction Steps

Run toolbox after disabling Docker

Feature Request

Make Toolbox independent from Docker

Desired Feature

Toolbox is independent from Docker

[euank]

The code in toolbox in question: https://github.com/coreos/toolbox/blob/a2767a0013c409a2381f7cdd4e31000b5fcded7e/toolbox#L33-L36

Since rkt, as of several releases ago, has an export command, it might be appropriate to use that there, though one regression it would introduce is requiring more space during extraction since it doesn't support streaming to stdout currently.

This would also be fixed with the change suggested in #1610

cc @lucab @dm0-

[glevand]

For this change to work on arm64 we need rkt/rkt#3526 (fetch: arch messed up) fixed.