Extend the virDomainDeviceAddress struture to allow disk controller addresses

Introduce a new structure

      struct _virDomainDeviceDriveAddress {
        unsigned int controller;
        unsigned int bus;
        unsigned int unit;
      };

and plug that into virDomainDeviceAddress and generates XML that
looks like

  <address type='drive' controller='1' bus='0' unit='5'/>

This syntax will be used by the QEMU driver to explicitly control
how drives are attached to the bus

* src/conf/domain_conf.h, src/conf/domain_conf.c: Parsing and
  formatting of drive addresses
* docs/schemas/domain.rng: Define new address format for drives

docs/schemas/domain.rng

@@ -1189,6 +1189,21 @@
       <ref name="pciFunc"/>
     </attribute>
   </define>
+  <define name="driveaddress">
+    <optional>
+      <attribute name="controller">
+        <ref name="driveController"/>
+      </attribute>
+    </optional>
+    <optional>
+      <attribute name="bus">
+	<ref name="driveBus"/>
+      </attribute>
+    </optional>
+    <attribute name="unit">
+      <ref name="driveUnit"/>
+    </attribute>
+  </define>
   <!--
       Devices attached to a domain.
     -->
@@ -1305,6 +1320,12 @@
 	  </attribute>
 	  <ref name="pciaddress"/>
 	</group>
+	<group>
+	  <attribute name="type">
+	    <value>drive</value>
+	  </attribute>
+	  <ref name="driveaddress"/>
+	</group>
       </choice>
     </element>
   </define>
@@ -1434,6 +1455,21 @@
       <param name="pattern">(0x)?[0-7]</param>
     </data>
   </define>
+  <define name="driveController">
+    <data type="string">
+      <param name="pattern">[0-9]{1,2}</param>
+    </data>
+  </define>
+  <define name="driveBus">
+    <data type="string">
+      <param name="pattern">[0-9]{1,2}</param>
+    </data>
+  </define>
+  <define name="driveUnit">
+    <data type="string">
+      <param name="pattern">[0-9]{1,2}</param>
+    </data>
+  </define>
   <define name="featureName">
     <data type="string">
       <param name='pattern'>[a-zA-Z0-9\-_]+</param>