[libvirt] Logging VM startup and shutdown

[Ed Swierk <eswierk bigswitch com>]

When troubleshooting a libvirt system the most obvious question I face
is when a given VM started and stopped.

The only way I've been able to obtain this information is by setting
log_level = 1 in libvirtd.conf, which turns on the firehose,
generating an enormous amount of output. I then have to sift through
the logs for magic strings like "virExecWithHook" to see when a VM
started, and "Shutting down VM" to see when a VM stopped. Is there no
concise message that indicates a VM starting up? "virExecWithHook"
doesn't exactly jump out.

I'd consider starting up and shutting down a VM to be at least worth
an info-level message in the log. I monkeyed with the log_filters
setting but I couldn't figure out how to filter those two strings. Any
hints?

--Ed