add CI job to test tftpboot

tests/tftpboot/test.nix

@@ -0,0 +1,31 @@
+{
+  liminix
+}:
+let derivation = (import liminix {
+      device = import "${liminix}/devices/qemu-armv7l/";
+      liminix-config = ./configuration.nix;
+    });
+    img = derivation.outputs.tftpboot;
+    pkgs = derivation.pkgs;
+    pkgsBuild = pkgs.pkgsBuildBuild;
+in pkgsBuild.runCommand "check" {
+  nativeBuildInputs = with pkgsBuild; [
+    expect
+    socat
+    run-liminix-vm
+  ] ;
+} ''
+mkdir vm
+ln -s ${img} result
+run-liminix-vm \
+ --background ./vm \
+ --u-boot ${pkgs.ubootQemuArm}/u-boot.bin \
+ --arch arm \
+ --flag -S \
+ --phram-address 0x40200000 \
+ --lan "user,tftp=`pwd`" \
+ --disk-image result/rootfs \
+ result/uimage result/rootfs
+
+expect ${./script.expect} 2>&1 |tee $out
+''