Move most of qemuProcessKill into virProcessKillPainfully

Move most of qemuProcessKill into virProcessKillPainfully

In the cgroups APIs we have a virCgroupKillPainfully function
which does the loop sending SIGTERM, then SIGKILL and waiting
for the process to exit. There is similar functionality for
simple processes in qemuProcessKill, but it is tangled with
the QEMU code. Untangle it to provide a virProcessKillPainfuly
function

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>