systemconfig: fix missing backslashes on env vars

pkgs/systemconfig/default.nix

@@ -92,10 +92,13 @@ in attrset:
         # case otherwise we will install into a ramfs/rootfs
         ""
       }
-      if test -d $dest/persist; then dest=$dest/persist; fi
+      if test -d \$dest/persist; then dest=\$dest/persist; fi
       cp -v -fP \$src/bin/* \$src/etc/* \$dest
       ${if attrset ? boot then ''
-        (cd \$dest && rm ./boot && ln -sf ${lib.strings.removePrefix "/" attrset.boot.target} ./boot)
+        (cd \$dest
+         if test -e boot ; then rm boot ; fi
+         ln -sf ${lib.strings.removePrefix "/" attrset.boot.target} ./boot
+        )
       '' else ""}
       EOF
       chmod +x $out/bin/install