Allow include=None to be passed to admin.backup.Info

This is forwarded to qubes.backup.Backup(), which uses None to choose
VMs according to their include_in_backups property.

('git show -w' recommended)

qubes/api/admin.py

@@ -1293,6 +1293,7 @@ class QubesAdminAPI(qubes.api.AbstractQubesAPI):
             dest_vm = profile_data['destination_vm']
             dest_path = profile_data['destination_path']
             include_vms = profile_data['include']
+            if include_vms is not None:
                 # convert old keywords to new keywords
                 include_vms = [vm.replace('$', '@') for vm in include_vms]
             exclude_vms = profile_data.get('exclude', [])
@@ -1339,6 +1340,9 @@ class QubesAdminAPI(qubes.api.AbstractQubesAPI):
                 'specify passphrase_text or passphrase_vm')
 
         # handle include
+        if include_vms is None:
+            vms_to_backup = None
+        else:
             vms_to_backup = set(vm for vm in self.app.domains
                 if any(qubes.utils.match_vm_name_with_special(vm, name)
                     for name in include_vms))