qemu: Support numad

numad is an user-level daemon that monitors NUMA topology and
processes resource consumption to facilitate good NUMA resource
alignment of applications/virtual machines to improve performance
and minimize cost of remote memory latencies. It provides a
pre-placement advisory interface, so significant processes can
be pre-bound to nodes with sufficient available resources.

More details: http://fedoraproject.org/wiki/Features/numad

"numad -w ncpus:memory_amount" is the advisory interface numad
provides currently.

This patch add the support by introducing a new XML attribute
for <vcpu>. e.g.

  <vcpu placement="auto">4</vcpu>
  <vcpu placement="static" cpuset="1-10^6">4</vcpu>

The returned advisory nodeset from numad will be printed
in domain's dumped XML. e.g.
  <vcpu placement="auto" cpuset="1-10^6">4</vcpu>

If placement is "auto", the number of vcpus and the current
memory amount specified in domain XML will be used for numad
command line (numad uses MB for memory amount):
  numad -w $num_of_vcpus:$current_memory_amount / 1024

The advisory nodeset returned from numad will be used to set
domain process CPU affinity then. (e.g. qemuProcessInitCpuAffinity).

If the user specifies both CPU affinity policy (e.g.
(<vcpu cpuset="1-10,^7,^8">4</vcpu>) and placement == "auto"
the specified CPU affinity will be overridden.

Only QEMU/KVM drivers support it now.

See docs update in patch for more details.

tests/domainsnapshotxml2xmlout/disk_snapshot.xml

@@ -28,7 +28,7 @@
     <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
     <memory unit='KiB'>219100</memory>
     <currentMemory unit='KiB'>219100</currentMemory>
-    <vcpu cpuset='1-4,8-20,525'>1</vcpu>
+    <vcpu placement='static' cpuset='1-4,8-20,525'>1</vcpu>
     <os>
       <type arch='i686' machine='pc'>hvm</type>
       <boot dev='hd'/>

tests/domainsnapshotxml2xmlout/full_domain.xml

@@ -11,7 +11,7 @@
     <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
     <memory unit='KiB'>219100</memory>
     <currentMemory unit='KiB'>219100</currentMemory>
-    <vcpu cpuset='1-4,8-20,525'>1</vcpu>
+    <vcpu placement='static' cpuset='1-4,8-20,525'>1</vcpu>
     <os>
       <type arch='i686' machine='pc'>hvm</type>
       <boot dev='hd'/>

tests/domainsnapshotxml2xmlout/metadata.xml

@@ -15,7 +15,7 @@
     </metadata>
     <memory unit='KiB'>219100</memory>
     <currentMemory unit='KiB'>219100</currentMemory>
-    <vcpu cpuset='1-4,8-20,525'>1</vcpu>
+    <vcpu placement='static' cpuset='1-4,8-20,525'>1</vcpu>
     <os>
       <type arch='i686' machine='pc'>hvm</type>
       <boot dev='hd'/>