QEMU crashes & burns if you try multiple Cirrus video cards, but
QXL copes fine. Adapt QEMU config code to allow multiple QXL
video cards

* src/qemu/qemu_conf.c: Support multiple QXL video cards

This supports the -spice argument posted for review against
the latest upstream QEMU/KVM. This supports the bare minimum
config with port, TLS port & listen address. The x509 bits are
added in a later patch.

* src/qemu_conf.c, src/qemu_conf.h: Add SPICE flag. Check for
  -spice availability. Format -spice arg for command line
* qemuhelptest.c: Add SPICE flag
* qemuxml2argvdata/qemuxml2argv-graphics-spice.args: Add <graphics>
  for spice
* qemuxml2argvdata/qemuxml2argv-graphics-spice.xml: Add -spice arg
* qemuxml2argvtest.c: Add SPICE flag

This supports the '-vga qxl' parameter in upstream QEMU/KVM
which has SPICE support added. This isn't particularly useful
until you get the next patch for -spice support. Also note that
while the libvirt XML supports multiple video devices, this
patch only supports a single one. A later patch can add support
for 2nd, 3rd, etc PCI devices for QXL

* src/qemu/qemu_conf.h: Flag for QXL support
* src/qemu/qemu_conf.c: Probe for '-vga qxl' support and implement it
* tests/qemuxml2argvtest.c, tests/qemuxml2xmltest.c,
  tests/qemuxml2argvdata/qemuxml2argv-graphics-spice.args,
  tests/qemuxml2argvdata/qemuxml2argv-graphics-spice.xml: Test
  case for generating spice args with RHEL6 kvm

To allow compatibility with older QEMU PCI device slot assignment
it is necessary to explicitly track the balloon device in the
XML. This introduces a new device

   <memballoon model='virtio|xen'/>

It can also have a PCI address, auto-assigned if necessary.

The memballoon will be automatically added to all Xen and QEMU
guests by default.

* docs/schemas/domain.rng: Add <memballoon> element
* src/conf/domain_conf.c, src/conf/domain_conf.h: parsing
  and formatting for memballoon device. Always add a memory
  balloon device to Xen/QEMU if none exists in XML
* src/libvirt_private.syms: Export memballoon model APIs
* src/qemu/qemu_conf.c, src/qemu/qemu_conf.h: Honour the
  PCI device address in memory balloon device
* tests/*: Update to test new functionality

Existing applications using libvirt are not aware of the disk
controller concept. Thus, after parsing the <disk> definitions
in the XML, it is neccessary to create <controller> elements
to satisfy all requested disks, as per their defined drive
addresses

* src/conf/domain_conf.c, src/conf/domain_conf.h,
  src/libvirt_private.syms: Add virDomainDefAddDiskControllers()
  method for populating disk controllers, and call it after
  parsing disk definitions.
* src/qemu/qemu_conf.c: Call virDomainDefAddDiskControllers()
  when doing ARGV -> XML conversion
* tests/qemuxml2argvdata/qemuxml2argv*.xml: Add disk controller
  data to all data files which don't have it already

When parsing the <disk> element specification, if no <address>
is provided for the disk, then automatically assign one based on
the <target dev='sdXX'/> device name. This provides for backwards
compatability with existing applications using libvirt, while also
allowing new apps to have complete fine grained control.

* src/conf/domain_conf.h, src/conf/domain_conf.c,
  src/libvirt_private.syms: Add virDomainDiskDefAssignAddress()
  for assigning a controller/bus/unit address based on disk target
* src/qemu/qemu_conf.c: Call virDomainDiskDefAssignAddress() after
  generating XML from ARGV
* tests/qemuxml2argvdata/*.xml: Add in drive address information
  to all XML files