views: Check form contain a cache partition

Make the partition and format form fail if the user has not added a
cache partition.

A cache partition is required to make the restoration of images work

ogcp/views.py

@@ -557,6 +557,14 @@ def action_setup_show():
 def action_setup_modify():
     form = SetupForm(request.form)
     if form.validate():
+        has_cache=False
+        for partition in form.partitions:
+            if partition.part_type.data == 'CACHE':
+                has_cache=True
+        if not has_cache:
+            flash(_(f'Missing cache partition'), category='error')
+            return redirect(url_for('commands'))
+
         ips = form.ips.data.split(' ')
 
         payload = {'clients': ips,