tests: Modify tests that print repr of an exception with 1 arg.

In Python 3.7 the behaviour of repr() of an exception with one argument
changed: it no longer prints a trailing comma in the argument list.  See
https://bugs.python.org/issue30399

This patch modifies tests that rely on this behaviour to not rely on it.
And the python34.py test is updated to include a test for this behaviour
with a .exp file.

tests/basics/dict1.py

@@ -27,7 +27,7 @@ print({1:1} == {2:1})
 try:
     {}[0]
 except KeyError as er:
-    print('KeyError', er, repr(er), er.args)
+    print('KeyError', er, er.args)
 
 # unsupported unary op
 try: