Automatic merge from submit-queue

Update images that use ubuntu-slim base image to :0.6

**What this PR does / why we need it**: `ubuntu-slim:0.4` is somewhat old, being based on Ubuntu 16.04, whereas `ubuntu-slim:0.6` is based on Ubuntu 16.04.1.

**Special notes for your reviewer**: I haven't pushed any of these images yet, so I expect all of the e2e builds to fail. If we're happy with the changes, I can push the images and then re-trigger tests.

**Release note**:

```release-note
NONE
```

cc @aledbf as FYI