Fix python3 issues with devstack

etree.tostring() needs to be massaged before calling libvirt's
baselineCPU or we will end up with a problem. This can be easily
recreated using:
http://paste.openstack.org/show/593069/
the fix was tested using:
http://paste.openstack.org/show/593070/

We need to send bytes to Popen.communicate under python3:
https://docs.python.org/3/library/subprocess.html?highlight=communicate#subprocess.Popen.communicate

Change-Id: I0ec47f99be8c3e4cb5ac5a6f7343354cc2de380c

nova/network/linux_net.py

@@ -371,7 +371,7 @@ class IptablesManager(object):
                         all_lines[start:end], table, table_name)
                 table.dirty = False
             self.execute('%s-restore' % (cmd,), '-c', run_as_root=True,
-                         process_input='\n'.join(all_lines),
+                         process_input=six.b('\n'.join(all_lines)),
                          attempts=5)
         LOG.debug("IPTablesManager.apply completed with success")
 

nova/virt/libvirt/host.py

@@ -714,8 +714,11 @@ class Host(object):
             if (hasattr(libvirt, 'VIR_CONNECT_BASELINE_CPU_EXPAND_FEATURES')
                 and self._caps.host.cpu.model is not None):
                 try:
+                    xml_str = self._caps.host.cpu.to_xml()
+                    if six.PY3:
+                        xml_str = xml_str.decode('utf-8')
                     features = self.get_connection().baselineCPU(
-                        [self._caps.host.cpu.to_xml()],
+                        [xml_str],
                         libvirt.VIR_CONNECT_BASELINE_CPU_EXPAND_FEATURES)
                     if features:
                         cpu = vconfig.LibvirtConfigCPU()

nova/virt/xenapi/firewall.py

@@ -30,6 +30,9 @@ class Dom0IptablesFirewallDriver(firewall.IptablesFirewallDriver):
     def _plugin_execute(self, *cmd, **kwargs):
         # Prepare arguments for plugin call
         args = {}
+        process_input = kwargs.get('process_input', None)
+        if process_input is not None and isinstance(process_input, bytes):
+            kwargs['process_input'] = process_input.decode('utf-8')
         args.update(map(lambda x: (x, str(kwargs[x])), kwargs))
         args['cmd_args'] = jsonutils.dumps(cmd)
         ret = self._session.call_plugin('xenhost.py', 'iptables_config', args)