Don't use apk cache to reduce image size

[t3easy]

The Problem/Issue/Bug:

Apk cache remains in image and makes it larger as it must be

How this PR Solves The Problem:

Use apk --no-cache parameter

Manual Testing Instructions:

Automated Testing Overview:

Related Issue Link(s):

Release/Deployment notes:

[CLAassistant]

All committers have signed the CLA.

[rickmanelius]

Added @rfay to review because I wasn't sure if there was a particular reason for this.

[rfay]

This looks great to me, thanks. I pushed this to drud/mariadb-local:20180627_mariadb_no_apk_cache - @t3easy if you could please add a commit setting that container in pkg/version/version.go it would be fantastic. Otherwise ask us to do it and tell us you don't mind us pushing into your fork.

[rfay]

I should note that this seems to reduce the image size by less than 1MB, so might not be as effective as you hoped. https://hub.docker.com/r/drud/mariadb-local/tags/

[andrewfrench]

Looks good to me, there's no reason to be pushing around a cache with the container image. Once @rfay's version.go request is in, this is good to pull.

[andrewfrench]

Just to confirm @rfay's point about the image size, here's a comparison of this version and the v0.20.0 image:

CONTAINER ID        IMAGE                         SIZE
340e94a2a9b6        drud/mariadb-local:v0.20.0    151MB (virtual 362MB)
d6918a2aceca        drud/mariadb-local:945-test   151MB (virtual 361MB)

I'd say the change is still valid either way, especially since I'm seeing --no-cache as a recommended flag when building an image. The compressed image size decreases from 64MB to 63MB.

[t3easy]

It's not dramatically but best practice.

Regarding

if you could please add a commit setting that container in pkg/version/version.go it would be fantastic

Just rais var DBTag = "v0.20.0" to v0.20.1?

[rfay]

var DBTag = 20180627_mariadb_no_apk_cache - the tag I pushed.

We use temporary tags between releases, when we release ddev v1.0.0 (the next one) we'll retag the latest version of the mariadb-local container to v1.0.0 to match the ddev version.

[rfay]

Looks good to me, thanks!