remove cpu feature duplications in libvirt

This patch fixes a bug in libvirt driver get_host_capabilities where
some features can be duplicated. In this patch we use the features returned
from baselineCPU as the only set of features.

Change-Id: Ib708e31e5ae14e93b384d2a8933079ca83ca8aaf
Closes-Bug: #1322702
Merge "remove cpu feature duplications in libvirt"