tools/kvm_stat: Add Python 3 support to kvm_stat

Make kvm_stat support Python 3 by changing the use of "print" to a
function rather than a statement, switching from "iteritems" and
"iterkeys" (removed in Python 3) to "items" and "keys" respectively,
and decoding bytes to strings when dealing with text.

With this change, kvm_stat is usable with Python 2.6 and greater.

Signed-off-by: Jeremy Cline <jeremy@jcline.org>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>