conf: Introduce new attribute for device address format

* src/conf/domain_conf.h: Add new member "target" to struct
  _virDomainDeviceDriveAddress.

* src/conf/domain_conf.c: Parse and format "target"

* Lots of tests (.xml) in tests/domainsnapshotxml2xmlout,
  tests/qemuxml2argvdata, tests/qemuxml2xmloutdata, and
  tests/vmx2xmldata/ are modified for newly introduced
  attribute "target" for address of "drive" type.

docs/formatdomain.html.in

@@ -1094,6 +1094,12 @@
       <target dev='hdc' bus='ide'/>
       <readonly/>
     </disk>
+    <disk type='block' device='lun'>
+      <driver name='qemu' type='raw'/>
+      <source dev='/dev/sda'/<
+      <target dev='sda' bus='scsi'/<
+      <address type='drive' controller='0' bus='0' target='3' unit='0'/<
+    </disk>
   </devices>
   ...</pre>
 
@@ -1401,8 +1407,9 @@
         Multifunction defaults to 'off'; any other value requires
         QEMU 0.1.3 and <span class="since">libvirt 0.9.7</span>.  For a
         "drive" controller, additional attributes
-        <code>controller</code>, <code>bus</code>,
-        and <code>unit</code> are available, each defaulting to 0.
+        <code>controller</code>, <code>bus</code>, <code>target</code>
+        (<span class="since">libvirt 0.9.11</span>), and <code>unit</code>
+        are available, each defaulting to 0.
       </dd>
       <dt><code>auth</code></dt>
       <dd>If present, the <code>auth</code> element provides the
@@ -1592,6 +1599,7 @@
       <dd>Drive addresses have the following additional
         attributes: <code>controller</code> (a 2-digit controller
         number), <code>bus</code> (a 2-digit bus number),
+        <code>target</code> (a 2-digit bus number),
         and <code>unit</code> (a 2-digit unit number on the bus).
       </dd>
       <dt><code>type='virtio-serial'</code></dt>

docs/schemas/domaincommon.rng

@@ -2459,6 +2459,11 @@
         <ref name="driveBus"/>
       </attribute>
     </optional>
+    <optional>
+      <attribute name="target">
+        <ref name="driveTarget"/>
+      </attribute>
+    </optional>
     <optional>
       <attribute name="unit">
         <ref name="driveUnit"/>
@@ -3147,6 +3152,11 @@
       <param name="pattern">[0-9]{1,2}</param>
     </data>
   </define>
+  <define name="driveTarget">
+    <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>