stack/erp5: SOFTWARE_HOME was incorrectly set to Zope2.egg/Zope2.

As SOFTWARE_HOME is added at the top of sys.path, this meant that Zope2.egg/Zope2
ended up at the top of sys.path:
  * This broke `imp.find_module('App')` and Pylint (`No name 'Extensions' in
    module 'App' (no-name-in-module)`) because there are `App` modules in both
    Zope2.egg/Zope2/ and Zope2.egg/ and the former was returned.
  * "Normal" instances and Products.ERP5Type.tests.runUnitTest properly set up
    SOFTWARE_HOME to Zope2.egg/.

Additionally, according to Zope2/Testing documentation, SOFTWARE_HOME is only
needed to find Zope2.egg/Testing module, already available as Zope2.egg is in
sys.path.

stack/erp5/buildout.cfg

@@ -327,12 +327,10 @@ entry-points =
   runUnitTest=runUnitTest:main
 scripts = runUnitTest
 initialization =
-  import glob, imp, os, sys
-  import App # prevent Testing from importing Zope2.App instead of App
+  import glob, os, sys
   import Products
   Products.__path__[:0] = filter(None,
     os.getenv('INSERT_PRODUCTS_PATH', '').split(os.pathsep))
-  os.environ['SOFTWARE_HOME'] = os.path.abspath(imp.find_module('Zope2')[1])
   os.environ['ZOPE_SCRIPTS'] = ''
   parts_directory = '''${buildout:parts-directory}'''
   repository_id_list = \
@@ -365,8 +363,6 @@ initialization =
   import sys
   import Products
   [Products.__path__.insert(0, p) for p in reversed(os.environ.get('INSERT_PRODUCTS_PATH', '').split(':')) if p]
-  import Zope2
-  os.environ['SOFTWARE_HOME'] = os.path.abspath(os.path.dirname(os.path.dirname(Zope2.__file__)))
   os.environ['ZOPE_SCRIPTS'] = ''
   repository_id_list = list(reversed('''${erp5_repository_list:repository_id_list}'''.split()))
   sys.path[0:0] = ['/'.join(['''${buildout:parts-directory}''', x]) for x in repository_id_list]