tools/kvm_stat: Add restart delay

If this service is enabled and the system rebooted, Systemd's initial
attempt to start this unit file may fail in case the kvm module is not
loaded. Since we did not specify a delay for the retries, Systemd
restarts with a minimum delay a number of times before giving up and
disabling the service. Which means a subsequent kvm module load will
have kvm running without monitoring.
Adding a delay to fix this.

Signed-off-by: Stefan Raspl <raspl@linux.ibm.com>
Message-Id: <20210325122949.1433271-1-raspl@linux.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>