This commit adds support for the High Precision Event Timer (HPET) for
x86 guests in the libvirt driver. The timer can be set by image property
'hw_time_hpet'. By default it remains turned off. When it is turned on
the HPET timer is activated in libvirt.
If the image property 'hw_time_hpet' is incorrectly set to a
non-boolean, the HPET timer remains turned off.
blueprint: support-hpet-on-guest
Change-Id: I3debf725544cae245fd31a8d97650392965d480a
Signed-off-by: Jack Ding <jack.ding@windriver.com>