Update xml schemas according to libvirt source

capability.rng: Guest features can be in any order.
nodedev.rng: Added <driver> element, <capability> phys_function and
virt_functions for PCI devices.
storagepool.rng: Owner or group ID can be -1.

schema tests: New capabilities and nodedev files; changed owner and
group to -1 in pool-dir.xml.
storage_conf: Print uid_t and gid_t as signed to storage pool XML.

tests/storagepoolxml2xmlout/pool-dir.xml

@@ -10,8 +10,8 @@
     <path>/var/lib/libvirt/images</path>
     <permissions>
       <mode>0700</mode>
-      <owner>0</owner>
-      <group>0</group>
+      <owner>-1</owner>
+      <group>-1</group>
       <label>some_label_t</label>
     </permissions>
   </target>