scripts: Unlink our temporary post scripts

I just happened to do an `ls /usr` on my workstation. Sigh 😣

Closes: #822
Approved by: jlebon

src/libpriv/rpmostree-scripts.c

@@ -220,6 +220,7 @@ run_script_in_bwrap_container (int rootfs_fd,
 
   ret = TRUE;
  out:
+  (void) unlinkat (rootfs_fd, postscript_path_host, 0);
   if (created_var_tmp)
     (void) unlinkat (rootfs_fd, "var/tmp", AT_REMOVEDIR);
   return ret;

tests/vmcheck/test-layering-scripts.sh

@@ -41,6 +41,9 @@ vm_reboot
 vm_assert_layered_pkg scriptpkg1 present
 echo "ok pkg scriptpkg1 added"
 
+vm_cmd "test ! -f /usr/scriptpkg1.posttrans"
+echo "ok no embarrassing crud leftover"
+
 # let's check that the group was successfully added
 vm_cmd getent group scriptpkg1
 echo "ok group scriptpkg1 active"