chore: migrate `jjb` agent image

This change adds the Docker image for the existing `jjb` Kubernetes
agent, which was previously maintained elsewhere. Some minor fixes to
home directory permissions are applied, but other than that the
Dockerfile remains identical.

Change-Id: Id291985dafc25faa6575e713879aac4b72a108bd
Signed-off-by: Chris Kay <chris.kay@arm.com>
2 files changed