lava: Make the AUM tests logs work again the web UI

Commit 39e6ec4f made `tar` output the extracted filenames while
deployng the overlays and later commit 39e6ec4f made it
customizable since the AUM tests do many reboot cycles each with their
own (redundant) overlay deployment, causing the logs to grow massively
and going over the limits imposed by the LAVA web UI, which refuses to
display them and only offers to download them in JSON format.

Unfortunately the fix on 39e6ec4f worked only partially and the
overlays in the loop were still upacked in verbose mode, resulting in
unreadable logs.

For some reason that currently escapes me related to the way Jinja2
imports work, re-importing the template with the macros from the
looping template fixes the issue.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

lava/common-boot-tpl-reboot.yaml

+{% import 'common-boot-macros.yaml' as boot with context -%}
   - boot:
       namespace: system
       timeout: