Ensure __pycache__ folder is deleted

When running python3, the cleanup of
the virtualenv is incomplete: While the *.pyc files are removed,
the python3 __pycache__ folder is not removed.

That causes the sed instruction (applying to files) to fail,
as the __pycache__ folder is not a regular file, but a folder.

With the sed not successfully running, the shebang of the
virtualenv is pointing to an incorrect location, causing then
a failure in keystone-manage commands.

On top of it, a success would happen should the last command
return 0. We now make sure the whole script must return
success.

This should fix the problem.

Change-Id: Id28fd1c4989bfff1d0d736c037b8f0e77eb082c1

tasks/keystone_install_source.yml

@@ -111,7 +111,9 @@
 # # to https://github.com/pypa/virtualenv/issues/565
 - name: Reset virtualenv and update its paths
   shell: |
+    set -o errexit
     find {{ keystone_bin }} -name \*.pyc -delete
+    if test -d {{ keystone_bin }}/__pycache__; then rmdir {{ keystone_bin }}/__pycache__; fi
     sed -si '1s/^.*python.*$/#!{{ keystone_bin | replace ('/','\/') }}\/python/' {{ keystone_bin }}/*
     virtualenv {{ keystone_bin | dirname }} \
         {{ (ansible_pkg_mgr == 'apt') | ternary('--always-copy', '') }} \