VirtualGraphics: Don't lookup local keymap over and over

Triggered with virt-manager: new vm -> customize before install with a
non qemu. Guest.get_xml_config copies each device so it can set defaults
in a non persistent way. Unfortunately VirtualGraphics was copied before
a keymap lookup was ever done. End result was that we called
util.default_keymap over and over which is slow and floods the logs.

virtinst/VirtualGraphics.py

@@ -127,6 +127,9 @@ class VirtualGraphics(VirtualDevice):
         if channels:
             self.channels = channels
 
+    def _cache(self):
+        # Make sure we've cached the _local_keymap value before copy()
+        self._default_keymap()
 
     def _default_keymap(self, force_local=False):
         if (not force_local and self.conn and

virtinst/XMLBuilderDomain.py

@@ -434,10 +434,20 @@ class XMLBuilderDomain(object):
         except:
             pass
 
+    def _cache(self):
+        """
+        This is a hook for classes to cache any state that is expensive
+        to lookup before we copy the object as part of Guest.get_xml_config.
+        Saves us from possibly doing the lookup over and over
+        """
+        pass
+
+
     def copy(self):
         # Otherwise we can double free XML info
         if self._is_parse():
             return self
+        self._cache()
         return copy.copy(self)
 
     def get_conn(self):