UBUNTU: [Packaging] install kvm_stat systemd service

UBUNTU: [Packaging] install kvm_stat systemd service

Install the kvm_stat systemd service in linux-host-tools package,
disabled by default.  The service logs KVM kernel module trace events to
/var/log/kvm_stat.csv.

This tool is useful for observing guest behavior from the host
perspective.  Often conclusions about performance or buggy behavior can
be drawn from the output.

BugLink: https://bugs.launchpad.net/bugs/1921870
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Guilherme Piccoli <gpiccoli@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>