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.


Change-Id: I4342ba198c70b92aa870edad0b560470747cd738
diff --git a/wrapper.py b/wrapper.py
index 9b782c4..e9556fe 100755
--- a/wrapper.py
+++ b/wrapper.py
@@ -19,4 +19,5 @@
 portage_path = os.path.join(base_path, 'lib', 'portage')
 sys.path.insert(0, os.path.join(portage_path, 'pym'))
 os.environ['PYTHONPATH'] = ':'.join(sys.path)
+os.environ['EPREFIX'] = '/'
 os.execv(os.path.join(portage_path, 'bin', os.path.basename(__file__)), sys.argv)