tools/kvm_stat: fix undue use of initial sleeptime

We should not use the initial sleeptime for any key press that does not
switch to a different screen, as that introduces an unaesthetic flicker due
to two updates in quick succession.

Signed-off-by: Stefan Raspl <raspl@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>