Create folders inside /mnt (w/o editing sierra_git.bb)

[jyijyi]

I remember i can overlay on read only file system.
For example,

mkdir /tmp/tmp_usr_lib;mkdir /tmp/tmp_usr_lib_wr;

mount -t overlay overlay /usr/lib -o lowerdir=/usr/lib,upperdir=/tmp/tmp_usr_lib,workdir=/tmp/tmp_usr_lib_wr;

Not sure if you can do the same.