wrapper: set EPREFIX by default

Portage is a bit limited in where it can have this variable set.
Stick it in the environment for all tools as that seems to work.

BUG=b:20895978

Change-Id: I4342ba198c70b92aa870edad0b560470747cd738
1 file changed
tree: 8961d555a473d4b52ba69c44ad29e24d0d6a5100
  1. .gitignore
  2. etc/
  3. usr/
  4. wrapper.py