Bring back kernel/snapd/gadget snaps revert/refresh jobs to the SRU t…

…est plan (BugFix) (canonical#1176)

Bring back kernel/snapd/gadget snaps revert/refresh jobs to the SRU test plan

The snap-refresh-revert nested part had been removed from the SRU test
plan in cd17d9a following some
discoveries that, when executed, the jobs executed would change the
system state in the wrong order (e.g. updating the kernel snap without
reverting it while running other jobs afterwards).

The jobs were modified to prevent this kind of scenario[1], and the use
of manifest entries[2] prevents the jobs from being run on all the
devices yet (currently, the only project that enables them is the Xinyi
project).

Fix LM-1522

[1] canonical#1124
[2]
https://github.com/canonical/checkbox/tree/main/providers/base/units/snapd#manifest-entries

providers/sru/units/sru.pxu

@@ -138,6 +138,7 @@ nested_part:
     # Now we ask to switch to the integrated graphics card.
     after-suspend-graphics-integrated-gpu-cert-automated
     # after-suspend-monitor-integrated-gpu-cert-automated # not defined
+    com.canonical.certification::snap-refresh-revert
 bootstrap_include:
     device
     graphics_card