[libvirt] util: log: How about online change logLevel?

[zhang bo]

Sometimes, when we encounter with a problem, we need to set libvirtd log level to DEBUG to dig detailed information.

But changing log level requires us to *restart* libvirtd.
    1) #vim /etc/libvirt/libvirtd.conf
        log_level = 1
    2) *service libvirtd restart*

We think that it makes sense to develop an API to *online* change log level, without restarting libvirtd.

What's your opinion? If it's necessary, I'd like to post a patch here.