vm/qemu: debug boot

Author: a-nogikh

vm/qemu/qemu.go

@@ -345,10 +345,14 @@ func (pool *Pool) Create(ctx context.Context, workdir string, index int) (vmimpl
 		if err := ctx.Err(); err != nil {
 			return nil, err
 		}
+		from := time.Now()
 		inst, err := pool.ctor(workdir, sshkey, sshuser, index)
+		log.Logf(0, "boot(idx=%d): attempt=%d took=%v err=%v",
+			index, i, time.Since(from), err)
 		if err == nil {
 			return inst, nil
 		}
+
 		if errors.Is(err, vmimpl.ErrCantSSH) {
 			// It is most likely a boot crash, just return the error as is.
 			return nil, err