util/qemu-error: prepend guest name to error message to identify affected VM owner

util/qemu-error: prepend guest name to error message to identify affected VM owner

This is followup patch to the one submitted back in Oct, 19

https://lists.gnu.org/archive/html/qemu-devel/2019-10/msg02102.html

My mistake here, I took my eyes of the mailing list after I got the
initial thumbs up. This patch follows up on Markus comments in the
above link.

Purpose of this patch:

We want to print guest name for errors, warnings and info messages. This
was the first of two patches the second being MCE errors targeting a VM
with guest name prepended. But in a large fleet we see many other
errors that disable a VM or crash it. In a large fleet and centralized
logging having the guest name enables identify of owner and customer.

Signed-off-by: Mario Smarduch <msmarduch@digitalocean.com>
Message-Id: <20200626201900.8876-1-msmarduch@digitalocean.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>