remote:service: Select RemoteSnappyRestartStrategy if SNAP_REVISION is set
In response to snapd CVE-2021-44731, the systemd checkbox service creates
a few "fake" snap runtime environment variables to still use wrapper_local
helpers.
Adding SNAP_REVISION in this module enforces the detection mechanism to
only select RemoteSnappyRestartStrategy if the service runs in snap confine.
Otherwise even with a fake SNAP_DATA, RemoteDebRestartStrategy must be selected.
session:assistant: Fix the detect_restart_strategy by looking into app_blob
The session title is not a reliable way to evaluate the session type.
By default launchers set the title to 'session title'.
This patch extract that information from the session metadata app blob.
This patch adds an optional arg to detect_restart_strategy so the information
that the session is remote can be used to pick the best strategy.
There's a bit of heuristic in the SessionAssistant class that guesses that the
session is remote by looking at its title - remote sessions have
'checkbox-slave' in the session's title.
restart.py: Check for RemoteDebRestartStrategy support first
Due to snapd CVE-2021-44731, the checkbox remote service now runs outside
confinement but fakes env var like SNAP and SNAP_DATA.
The auto detection mechanism must check the RemoteDebRestartStrategy first
because the new systemd service is also named checkbox-ng.service like for
debian packages.
Sharing the same restart strategy logic as debs can only work if the code
using on_ubuntucore() is never reached in this use case.
