Fix no busybox symlinks issue on rhel

busybox on rhel has no `--list' option, which cause populate_busybox
can not create busybox symlinks. So the ramdisk created will not work
totally.

Fixes bug #1257669

Change-Id: I4f905673bb577867c99e0ccc0756c56a292474f5
Merge "Fix no busybox symlinks issue on rhel"