Use closest CPU model when decoding from CPUID

Use closest CPU model when decoding from CPUID

Current implementation of x86Decode() used for CPUID -> model+features
translation does not always select the closest CPU model. When walking
through all models from cpu_map.xml the function considers a new
candidate as a better choice than a previously selected candidate only
if the new one is a superset of the old one. In case the new candidate
is closer to host CPU but lacks some feature comparing to the old
candidate, the function does not choose well.

This patch changes the algorithm so that the closest model is always
selected. That is, the model which requires the lowest number of
additional features to describe host CPU.

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