tools/kvm_stat: handle SIGINT in log and batch modes

SIGINT causes ugly unhandled exceptions in log and batch mode, which we
prevent by catching the exceptions accordingly.

Signed-off-by: Stefan Raspl <raspl@linux.vnet.ibm.com>
Reviewed-by: Marc Hartmayer <mhartmay@linux.vnet.ibm.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>