Clean apt-get to reduce image size

[stp-ip]

Reduces image sizes by another 7 MB each.

[stp-ip]

Removed cleanup command and reassured tabs are used.

[tianon]

I think the 7MB is coming entirely from /var/lib/apt/lists - I've run some tests locally with a container and using docker diff <container> to check what's changed, and /var/cache/apt is created, but nothing in it ever sticks around after the apt-get install completes.

root@45a24dc9b5db:/# du -hs /var/lib/apt/lists 
8.0M    /var/lib/apt/lists

[stp-ip]

Cache doesn't keep things around most of the time. I added it for rare edge cases and to show more general best practices. But if need be I can edit it out.

[tianon]

So, the Debian images all have this: https://github.com/docker/docker/blob/1aa67071cb3e6bc8a08f662d913cdb1b1eda1645/contrib/mkimage/debootstrap#L82-L83

Don't Dir::Cache::pkgcache and Dir::Cache::srcpkgcache essentially disable the cache entirely?

[stp-ip]

@tianon so your take would be to just remove the cache removal anyway?

[tianon]

Yeah, since it isn't really buying us anything like the lists removal does.

[stp-ip]

Pushed the latest change and squashed all commits.

[yosifkit]

LGTM

[tianon]

LGTM

[tianon]

Thanks :smile: