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/try_as_var.py

@@ -1,7 +1,7 @@
 try:
     raise ValueError(534)
 except ValueError as e:
-    print(repr(e))
+    print(type(e), e.args)
 
 # Var bound in except block is automatically deleted
 try: