Specify -cpu host to pass through cpu capabilities to the host.

I hit a problem trying to run a new version of signal-cli via a KVM guest. Signal CLI now requires the x86-64-v2 cpu capability (this command lists the CPU capabilities on host and guest: /lib64/ld-linux-x86-64.so.2 --help | grep supported as documented here: https://packaging.gitlab.io/signal-cli/installation/standalone/).

I have the CPU capability on the host, but not the guest.

If I add -cpu host to the kvm command (which means pass through all capabilities on the host to the kvm guest), then I get what I need.

It seems that the default setting is 'qemu64' and the recommended setting is 'host'.

@dkg - Do you see any reason not to add -cpu host to kvm-start?