fix(bundle.bbclass): varflags expansion in python anonymous function

Python anonymous functions are evaluated before `=` which expand
the final variable value. This fix set the `getVarFlags` kwarg `expand`
to `True` (default is `False`) to be able to assign varflag
with bitbake variable (`${...}`) or python inline syntax (`${@...})`.

Signed-off-by: Jean-Pierre Geslin <jarsop@outlook.com>

classes-recipe/bundle.bbclass

@@ -142,7 +142,9 @@ RAUC_BUNDLE_FORMAT[doc] = "Specifies the bundle format to be used (plain/verity)
 python __anonymous() {
     d.appendVarFlag('do_unpack', 'vardeps', ' RAUC_BUNDLE_HOOKS')
     for slot in (d.getVar('RAUC_BUNDLE_SLOTS') or "").split():
-        slotflags = d.getVarFlags('RAUC_SLOT_%s' % slot)
+        # We have to expand the slotflags here as python anonymous functions
+        # are executed before `=` assignments are evaluated.
+        slotflags = d.getVarFlags('RAUC_SLOT_%s' % slot, expand=True)
         imgtype = slotflags.get('type') if slotflags else None
         if not imgtype:
             bb.debug(1, "No [type] given for slot '%s', defaulting to 'image'" % slot)