features: fix serialization

qubesd_call expect "bytes" type. Additionally serialize false value as
empty string (which is treated by python as false value), because
otherwise would be serialized to (non-empty) string, which is true value
in python.

qubesadmin/features.py

@@ -42,7 +42,12 @@ class Features(object):
         self.vm.qubesd_call(self.vm.name, 'admin.vm.feature.Remove', key)
 
     def __setitem__(self, key, value):
-        self.vm.qubesd_call(self.vm.name, 'admin.vm.feature.Set', key, value)
+        if not value:
+            # False value needs to be serialized as empty string
+            self.vm.qubesd_call(self.vm.name, 'admin.vm.feature.Set', key, b'')
+        else:
+            self.vm.qubesd_call(self.vm.name, 'admin.vm.feature.Set', key,
+                str(value).encode())
 
     def __getitem__(self, item):
         return self.vm.qubesd_call(

qubesadmin/tests/tools/qvm_features.py

@@ -51,7 +51,7 @@ class TC_00_qvm_features(qubesadmin.tests.QubesTestCase):
             b'0\x00some-vm class=AppVM state=Running\n'
         self.app.expected_calls[
             ('some-vm', 'admin.vm.feature.Set',
-             'feature3', 'value of feature')] = b'0\x00'
+             'feature3', b'value of feature')] = b'0\x00'
         self.assertEqual(
             qubesadmin.tools.qvm_features.main(['some-vm', 'feature3',
                 'value of feature'],