slapos.cookbook: don't use 'sh -e' shebang in createWrapper

This partially reverts f834a06f.

This shebang was causing issues with testnodes. See
f834a06f (comment 228158)

slapos/recipe/librecipe/generic.py

@@ -169,7 +169,7 @@ class GenericBaseRecipe(object):
     # here (note that this can't be done correctly with a POSIX shell, because
     # the process can't be given a name).
 
-    lines = ['#!/bin/sh -e']
+    lines = ['#!/bin/sh']
 
     if sig_ign:
       lines.append("trap '' " + sig_ign)