login: Do not dereference proot binds /bin and /etc

`/bin` and `/etc` are symlinks to `/system/bin` and `/system/etc`, by
default proot will dereference and override them with new contents.

After this change, `/system/bin` and `/system/etc` are kept untouched,
so commands like `/system/bin/ping` can be run directly.

AUTHORS

@@ -2,3 +2,4 @@ Alexander Sosedkin <monk@unboiled.info>
 Tobias Happ <tobias.happ@gmx.de>
 Bruno Bigras <bigras.bruno@gmail.com>
 Evgeny Kurnevsky <kurnevsky@gmail.com>
+Zhong Jianxin <azuwis@gmail.com>

modules/environment/login/login.nix

@@ -48,8 +48,8 @@ writeScript "login" ''
 
   exec ${installationDir}/bin/proot-static \
     -b ${installationDir}/nix:/nix \
-    -b ${installationDir}/bin:/bin \
-    -b ${installationDir}/etc:/etc \
+    -b ${installationDir}/bin:/bin! \
+    -b ${installationDir}/etc:/etc! \
     -b ${installationDir}/tmp:/tmp \
     -b ${installationDir}/usr:/usr \
     -b ${installationDir}/dev/shm:/dev/shm \