Create busybox commands as symlinks instead of hardlinks

Create busybox commands as symlinks instead of hardlinks

I was getting a "Too many links" error when creating a busybox container on
a btrfs file system. This change has the template create the links as
symlinks instead. It also generates the list of commands to be symlinked from
busybox itself instead of a hardcoded list in the template.

Also set the root password to root, to match what other templates do.

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>