libxl, Introduce the command line handler for the new qemu.

libxl, Introduce the command line handler for the new qemu.
From: Anthony PERARD <anthony.perard@citrix.com>

This patch adds a function to check the version of the device model.
Depending on the version of the DM, the command line arguments will be
built differently.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 tools/libxl/libxl.c       |  160 ++++++++++++++++++++++++++++++++++++++++++++-
 tools/libxl/libxl_utils.c |   78 ++++++++++++++++++++++
 tools/libxl/libxl_utils.h |    6 ++
 3 files changed, 243 insertions(+), 1 deletions(-)