pypy: fix failing test files with Pypy5.6.0 stable

pypy: fix failing test files with Pypy5.6.0

Pypy 5.6.0 saves cached bytecode files in __pycache__ directory, clean them in
tests to fix loading old test extensions code.

Doing so should also helps for Python3.x migration.

--- a/tests/test-commandserver.t	Sun Jul 30 12:19:46 2017 +0530
+++ b/tests/test-commandserver.t	Mon Jul 31 17:43:45 2017 +0200
@@ -234,7 +234,9 @@
   *** runcommand --config hooks.pre-identify=python:hook.hook id
   eff892de26ec tip
 
+Clean hook cached version
   $ rm hook.py*
+  $ rm -Rf __pycache__
 
   $ echo a >> a
   >>> import os

--- a/tests/test-fncache.t	Sun Jul 30 12:19:46 2017 +0530
+++ b/tests/test-fncache.t	Mon Jul 31 17:43:45 2017 +0200
@@ -270,7 +270,11 @@
   > cmdtable = {}
   > 
   > EOF
+
+Clean cached version
   $ rm -f "${extpath}c"
+  $ rm -Rf "`dirname $extpath`/__pycache__"
+
   $ touch z
   $ hg ci -qAm z
   transaction abort!
@@ -305,7 +309,11 @@
   > cmdtable = {}
   > 
   > EOF
+
+Clean cached versions
   $ rm -f "${extpath}c"
+  $ rm -Rf "`dirname $extpath`/__pycache__"
+
   $ hg up -q 1
   $ touch z
   $ hg ci -qAm z 2>/dev/null