[libvirt] [RFC] Support changing scheduler setting persistently

[Osier Yang]

This patch series introduce a new API virDomainSetSchedulerParametersFlags
to change the scheduler setting persistently.

The new API accepts two flags, VIR_DOMAIN_SCHED_PARAMS_LIVE and
VIR_DOMAIN_SCHED_PARAMS_PERSISTENT, "LIVE" flag affects the running domain
config, "PERSISTENT" affects both the running and persistent domain config,
both flags require the domain is running. "LIVE" flags is used by default.

It's not like "setvcpus", which accepts "--live", "--config", and "--current"
flags, as scheduler setting relates with cgroup (QEMU/LXC), upper layer apps
probably need to use virDomainGetSchedulerParameter and virDomainSetSchedulerParametersFlags
together, such as virsh, virDomainGetSchedulerParameter looks up parameters,
so support changing the scheduler setting on inactive domain probably is not
good idea.

Regards
Osier