Implement CPU topology support for QEMU driver

Implement CPU topology support for QEMU driver

QEMU's command line equivalent for the following domain XML fragment
    <vcpus>2</vcpus>
    <cpu ...>
        ...
        <topology sockets='1' cores='2', threads='1'/>
    </cpu>

is

    -smp 2,sockets=1,cores=2,threads=1

This syntax was introduced in QEMU-0.12.

Version 2 changes:
- -smp argument build split into a separate function
- always add ",sockets=S,cores=C,threads=T" to -smp if qemu supports it
- use qemuParseCommandLineKeywords for command line parsing

Version 3 changes:
- ADD_ARG_LIT => ADD_ARG and line reordering in qemudBuildCommandLine
- rebased

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>