Fix using filter() to meet python2,3

As mentioned in link[1], if we need filter on python3,
Replace filter(lambda obj: test(obj), data) with:
[obj for obj in data if test(obj)].

[1] https://wiki.openstack.org/wiki/Python3

Change-Id: Ie484ccd7ef0428313a29e9ef6930ebb2646ee879

nova/tests/unit/objects/test_instance.py

@@ -147,7 +147,7 @@ class _TestInstanceObject(object):
         exp_cols.remove('migration_context')
         exp_cols.remove('keypairs')
         exp_cols.remove('device_metadata')
-        exp_cols = list(filter(lambda x: 'flavor' not in x, exp_cols))
+        exp_cols = [exp_col for exp_col in exp_cols if 'flavor' not in exp_col]
         exp_cols.extend(['extra', 'extra.numa_topology', 'extra.pci_requests',
                          'extra.flavor', 'extra.vcpu_model',
                          'extra.migration_context', 'extra.keypairs',

nova/tests/unit/virt/libvirt/test_firewall.py

@@ -255,8 +255,7 @@ class IptablesFirewallTestCase(test.NoDBTestCase):
         self.fw.prepare_instance_filter(instance_ref, network_model)
         self.fw.apply_instance_filter(instance_ref, network_model)
 
-        in_rules = filter(lambda l: not l.startswith('#'),
-                          self.in_rules)
+        in_rules = [l for l in self.in_rules if not l.startswith('#')]
         for rule in in_rules:
             if 'nova' not in rule:
                 self.assertIn(rule, self.out_rules,

nova/tests/unit/virt/vmwareapi/fake.py

@@ -232,7 +232,7 @@ class ManagedObject(object):
 
     def delete(self, attr):
         """Deletes an attribute."""
-        self.propSet = filter(lambda elem: elem.name != attr, self.propSet)
+        self.propSet = [elem for elem in self.propSet if elem.name != attr]
 
     def __setattr__(self, attr, val):
         # TODO(hartsocks): this is adds unnecessary complexity to the class

nova/tests/unit/virt/xenapi/test_xenapi.py

@@ -2728,8 +2728,7 @@ class XenAPIDom0IptablesFirewallTestCase(stubs.XenAPITestBase):
         return secgroup
 
     def _validate_security_group(self):
-        in_rules = filter(lambda l: not l.startswith('#'),
-                          self._in_rules)
+        in_rules = [l for l in self._in_rules if not l.startswith('#')]
         for rule in in_rules:
             if 'nova' not in rule:
                 self.assertIn(rule, self._out_rules,