Add "latest" tag to images in order to match example commands.
Add "latest" tag to images in order to match example commands.

A "latest tag is now added to the docker images being built so that the
tag can be used properly in the example commands of the admin guide.

Signed-off-by: Kai Hudalla <6c3288b94355003a6c5f12ba233f9fc06ef02a62@bosch-si.com>
dejanb/hono,dejanb/hono,dejanb/hono