Allow to use embedded lib in embedded lib

For example, if you have the following scripts in an image:
lib/
   |- 01-foo.py  (module 'foo')
   |- 02-bar.py  (module 'bar')
module 'bar' (and subsequent) could import and use content from module 'foo'.

Signed-off-by: Sébastien Luttringer <sebastien.luttringer@smartjog.com>