libvirt: safe_decode xml for i18n logging

The xml argument passed to _create_domain can be a utf-8 encoded string
which causes a UnicodeDecodeError when it is substituted into the _LE
unicode translated message. Safely decoding the xml argument before
attempting to substitute it into the error message avoids the
UnicodeDecodeError.

(cherry picked from commit 96a2283c1a)

Conflicts:

	nova/tests/unit/virt/libvirt/test_driver.py
	nova/virt/libvirt/driver.py

Change to strutils (instead of encodeutils) and test is located in
"tests/" instead of "tests/unit/".

Closes-Bug: #1453274
Change-Id: I4cf1836f4ca9097f7c6d98c5212a14d24111fe67

nova/tests/virt/libvirt/test_driver.py

@@ -9364,12 +9364,17 @@ Active:          8381604 kB
             self.assertEqual(fake_xml, xml)
             raise libvirt.libvirtError('virDomainDefineXML() failed')
 
+        def fake_safe_decode(text, *args, **kwargs):
+            return text + 'safe decoded'
+
         self.log_error_called = False
 
         def fake_error(msg, *args):
             self.log_error_called = True
             self.assertIn(fake_xml, msg % args)
+            self.assertIn('safe decoded', msg % args)
 
+        self.stubs.Set(strutils, 'safe_decode', fake_safe_decode)
         self.stubs.Set(nova.virt.libvirt.driver.LOG, 'error', fake_error)
 
         self.create_fake_libvirt_mock(defineXML=fake_defineXML)

nova/virt/libvirt/driver.py

@@ -4370,7 +4370,8 @@ class LibvirtDriver(driver.ComputeDriver):
         err = None
         try:
             if xml:
-                err = _LE('Error defining a domain with XML: %s') % xml
+                err = (_LE('Error defining a domain with XML: %s') %
+                       strutils.safe_decode(xml, errors='ignore'))
                 domain = self._conn.defineXML(xml)
 
             if power_on: