Windows instances require the timezone to be "localtime"

This was relatively simple to fix, assuming that the image used
to boot the windows instance has the os_type set to "windows".
The use of os_type in this manner is consistent with the
existing use in the Xen hypervisor driver.

DocImpact: if you're booting windows instances, then you need to
set the os_type image property in glance to "windows". Otherwise
your instances will have their clock timezone set to UTC, which
has unexpected side effects in windows.

(cherry picked from commit 280a336)
(cherry picked from commit 18de647)

Conflicts:
	nova/virt/libvirt/driver.py

Note that the unit test had to be tweaked to work in the backport.
There are no functional changes however.

Change-Id: Id6759a290ed25c9add97ac61bb7d165b3fb908b2
Closes-Bug: 1231254

nova/tests/test_libvirt.py

@@ -608,6 +608,19 @@ def test_get_guest_config(self):
         self.assertEquals(cfg.clock.timers[1].tickpolicy,
                           "catchup")
 
+    def test_get_guest_config_windows(self):
+        conn = libvirt_driver.LibvirtDriver(True)
+        instance_ref = db.instance_create(self.context, self.test_instance)
+        instance_ref['os_type'] = 'windows'
+
+        cfg = conn.get_guest_config(instance_ref,
+                                    _fake_network_info(self.stubs, 1),
+                                    None, None)
+
+        self.assertEquals(type(cfg.clock),
+                          config.LibvirtConfigGuestClock)
+        self.assertEquals(cfg.clock.offset, "localtime")
+
     def test_get_guest_config_with_two_nics(self):
         conn = libvirt_driver.LibvirtDriver(True)
         instance_ref = db.instance_create(self.context, self.test_instance)

nova/virt/libvirt/driver.py

@@ -1801,8 +1801,17 @@ def get_guest_config(self, instance, network_info, image_meta, rescue=None,
             guest.acpi = True
             guest.apic = True
 
+        # NOTE(mikal): Microsoft Windows expects the clock to be in
+        # "localtime". If the clock is set to UTC, then you can use a
+        # registry key to let windows know, but Microsoft says this is
+        # buggy in http://support.microsoft.com/kb/2687252
         clk = config.LibvirtConfigGuestClock()
-        clk.offset = "utc"
+        if instance['os_type'] == 'windows':
+            LOG.info(_('Configuring timezone for windows instance to '
+                       'localtime'), instance=instance)
+            clk.offset = 'localtime'
+        else:
+            clk.offset = 'utc'
         guest.set_clock(clk)
 
         if FLAGS.libvirt_type == "kvm":