Include system logs in /var/log in diagnostic file

Include all the logs in /var/log when generating a diagnostic file. Hopefully this will give me more insights into the system.

assigned to @agent_kith

moved from snakeoil-rest#179 (moved)

changed milestone to %99.0.0

changed milestone to %99.0.0 (Backlog)

added In Dev label

changed milestone to %1.2.5 (Gear Isolation U5)

unassigned @agent_kith

removed In Dev label

created branch 26-include-system-logs-in-var-log-in-diagnostic-file to address this issue

assigned to @agent_kith

mentioned in commit 2798a5dc

mentioned in merge request !14 (merged)

closed with commit 99308de4