kvm tools: Beautify kvm list output

kvm tools: Beautify kvm list output

With the patch, output of "kvm list" will be:

% ./kvm list
   PID NAME                 STATE
------------------------------------
 5270 test                 running
      test                 shut off
      default              shut off

"not running" is changed into "shut off", as it might
be other states which are "not running" in future? such
as "paused".

Signed-off-by: Osier Yang <jyang@redhat.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>