Make the libvirt trace compact: libvirt API names, one error field, terse test output

The first live run showed the trace working but noisy: testr printed
ts/level/msg and the per-run constants on every line, the error text
appeared twice, host appeared twice on image-cache lines, and the Go
method name was less useful than the libvirt function it maps to.

The tracer now logs rpc=virDomainLookupByName (go-libvirt's names are the
public API names without the vir prefix), error plus libvirtError (code
name) and libvirtCode, and image.go stops re-adding host. The integration
test replaces testr with a compact logr sink: time, logger name, the rpc
as headline, then fields, with provider/host/name omitted since the first
line of the run states them. Docs and execution log updated.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/kvm-provider.md

@@ -194,10 +194,11 @@ The provider logs through controller-runtime's logger, named `kvm`, with
 - `--zap-log-level=debug` (logr V(1)): one line per provider operation
   (`domain defined`, `KVM domain ensured running`, ...) **and one
   `libvirt call` line per libvirt RPC**, named `kvm.libvirt`, with
-  `method`, the identifiers it was given (`domain`, `pool`, `volume`),
-  curated results (`state`, `path`, `interfaces`), `duration`, and on
-  failure `error` plus `libvirtCode`, `libvirtCodeName` and
-  `libvirtMessage`. Connection events (`libvirt host connected`, dial
+  `rpc` (the libvirt API function, e.g. `virDomainLookupByName`), the
+  identifiers it was given (`domain`, `pool`, `volume`), curated results
+  (`state`, `path`, `interfaces`), `duration`, and on failure `error`
+  plus `libvirtError` (the code name, e.g. `ErrNoDomain`) and
+  `libvirtCode`. Connection events (`libvirt host connected`, dial
   failures, `libvirt connection dropped` with a reason) log at the same
   level. A Create is about ten RPCs; a Get is four.
 - `--zap-log-level=2`: the same lines also carry the domain and volume