add result/install.sh to systemConfiguration output

this makes it possible to install a systemconfig instead of
having to use nix-shell (which is very slow)

pkgs/systemconfig/build-system-install.sh

@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+
+# this shell script can be run on the build system to
+# min-copy-closure the system configuration onto the device
+# and reboot/restart services as requested
+
+die() {
+    echo "$@"
+    exit 1
+}
+
+PATH=@min-copy-closure@/bin:$PATH
+
+ssh_command=${SSH_COMMAND-ssh}
+
+reboot="reboot"
+
+case "$1" in
+    "--no-reboot")
+	unset reboot
+	shift
+	;;
+    "--fast")
+	reboot="soft"
+	shift
+	;;
+esac
+
+target_host=$1
+shift
+
+test -n "$target_host" || \
+    die "Usage: $0 [--no-reboot] [--fast] target-host"
+
+toplevel=$(cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
+test -e $toplevel/etc/nix-store-paths || die "missing etc/nix-store-paths, is this really a system configuration?"
+echo installing from systemConfiguration $toplevel to host $target_host
+
+min-copy-closure $target_host $toplevel
+$ssh_command $target_host $toplevel/bin/install
+case "$reboot" in
+    reboot)
+	$ssh_command $target_host "sync; source /etc/profile; reboot"
+	;;
+    soft)
+	$ssh_command $target_host $toplevel/bin/restart-services
+	;;
+    *)
+	;;
+esac

pkgs/systemconfig/default.nix

@@ -7,6 +7,7 @@
 {
   writeText,
   writeFennel,
+  buildPackages,
   lib,
   s6-init-bin,
   closureInfo,
@@ -82,6 +83,8 @@ in attrset:
       $STRIP --remove-section=.note  --remove-section=.comment --strip-all makedevs -o $out/bin/activate
       ln -s ${s6-init-bin}/bin/init $out/bin/init
       cp -p ${writeFennel "restart-services" {} ./restart-services.fnl} $out/bin/restart-services
+      substitute ${./build-system-install.sh} $out/install.sh --subst-var-by min-copy-closure ${buildPackages.min-copy-closure}
+      chmod +x $out/install.sh
       cat > $out/bin/install <<EOF
       #!/bin/sh -e
       prefix=\''${1-/}