Add a --to option to build_image

src/scripts/enter_chroot.sh

Index: src/scripts/enter_chroot.sh
diff --git a/src/scripts/enter_chroot.sh b/src/scripts/enter_chroot.sh
index 33aad4bea3ef67e493c0805b4fcfd1f9177fadca..6ad51fa44c251f4e11f8f478994c19e320481bc4 100755
--- a/src/scripts/enter_chroot.sh
+++ b/src/scripts/enter_chroot.sh
@@ -84,6 +84,13 @@ function setup_env {
           die "Could not mount $MOUNTED_PATH"
     fi
 
+    MOUNTED_PATH="$(readlink -f "$FLAGS_chroot/sys")"
+    if [ -z "$(mount | grep -F "on $MOUNTED_PATH ")" ]
+    then
+      sudo mount none -t sysfs "$MOUNTED_PATH" || \
+          die "Could not mount $MOUNTED_PATH"
+    fi
+
     MOUNTED_PATH="$(readlink -f "$FLAGS_chroot/dev/pts")"
     if [ -z "$(mount | grep -F "on $MOUNTED_PATH ")" ]
     then