o/t/ktest: switch to proper rule

This was previously implemented as a macro, lacking proper transitions.
Reimplement it as a proper test rule.

Change-Id: I237a2fcc29ea6dfbb294ce6313c9ff457def12b8
Reviewed-on: https://review.monogon.dev/c/monogon/+/3722
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
Tested-by: Jenkins CI
diff --git a/osbase/test/launch/launch.go b/osbase/test/launch/launch.go
index cf165a1..df84e7d 100644
--- a/osbase/test/launch/launch.go
+++ b/osbase/test/launch/launch.go
@@ -294,7 +294,7 @@
 	}
 
 	var stdErrBuf bytes.Buffer
-	cmd := exec.CommandContext(ctx, "qemu-system-x86_64", append(baseArgs, extraArgs...)...)
+	cmd := exec.CommandContext(ctx, "/usr/bin/qemu-system-x86_64", append(baseArgs, extraArgs...)...)
 	cmd.Stdout = opts.SerialPort
 	cmd.Stderr = &stdErrBuf