tools/kvm_stat: fix python3 issues

Python3 returns a float for a regular division - switch to a division
operator that returns an integer.
Furthermore, filters return a generator object instead of the actual
list - wrap result in yet another list, which makes it still work in
both, Python2 and 3.

Signed-off-by: Stefan Raspl <raspl@linux.ibm.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>