fix(ex_handling): Don't let finally block mask ex

We have a project with test code which utilizes collective.solr which
utilizes collective.indexing which pushes index operations to the
pre commit phase.
In our case an exception was then thrown during commit within
the zopeApp context.
closing the connection in the finally statement raised another exception
because of the unclean state left by the first exception.
This exception in the finally block totally masked the original
exception, hindering bug fixing.

CHANGES.rst

@@ -4,7 +4,8 @@ Changelog
 4.0.15 (unreleased)
 -------------------
 
-- Nothing changed yet.
+- Prevent exception masking in finally clause of zopeApp context
+  [do3cc]
 
 
 4.0.14 (2015-07-29)

src/plone/testing/z2.py

@@ -253,18 +253,37 @@ def zopeApp(db=None, connection=None, environ=None):
     if connection is None:
         connection = app._p_jar
 
+    # exceptions in finally clauses can mask exceptions
+    # in the preceeding code block. So we catch
+    # every exception and throw it instead of the exception
+    # in the finally clause
+    inner_exception = None
     try:
         yield app
-    except:
-        transaction.abort()
+    except Exception, e:
+        inner_exception = e
+        try:
+            transaction.abort()
+        except Exception, e:
+            inner_exception = e
+            raise
         raise
     else:
-        transaction.commit()
+        try:
+            transaction.commit()
+        except Exception, e:
+            inner_exception = e
     finally:
-        app.REQUEST.close()
-
-        if closeConn:
-            connection.close()
+        try:
+            app.REQUEST.close()
+
+            if closeConn:
+                connection.close()
+        except:
+            if inner_exception:
+                raise inner_exception
+            else:
+                raise
 
 # Startup layer - you probably don't want to use this one directly