Backend: add /dev/random workaround for recovery

- per Chainfire, "fix slow RNG on some devices, which may cause installation to take weeks"
- it seems like this issue may have been triggered now in recovery on some devices by some of the changes from the new mounting rewrite

META-INF/com/google/android/update-binary

@@ -75,7 +75,8 @@ restore_env() {
   test "$savedpre" && export LD_PRELOAD="$savedpre";
   umount_all;
   ($bb mv -f /system_link /system;
-  $bb mv -f /system_root_link /system_root) 2>/dev/null;
+  $bb mv -f /system_root_link /system_root;
+  $bb umount -l /dev/random) 2>/dev/null;
 }
 abort() {
   ui_print "$@";
@@ -128,6 +129,7 @@ if [ -f version ]; then
 fi;
 ui_print " " "AnyKernel3 by osm0sis @ xda-developers" " " " ";
 
+$BOOTMODE || $bb mount -o bind /dev/urandom /dev/random;
 umount_all;
 setup_mountpoint $ANDROID_ROOT;
 if ! is_mounted $ANDROID_ROOT; then