Ensure __pycache__ folder is deleted

In some cases 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: I2999f9253e8bb70854e02768aef13f3b57839987

tasks/heat_install_source.yml

@@ -93,7 +93,9 @@
 # to https://github.com/pypa/virtualenv/issues/565
 - name: Update virtualenv path
   shell: |
+    set -o errexit
     find {{ heat_bin }} -name \*.pyc -delete
+    if test -d {{ heat_bin }}/__pycache__; then rmdir {{ heat_bin }}/__pycache__; fi
     sed -si '1s/^.*python.*$/#!{{ heat_bin | replace ('/','\/') }}\/python/' {{ heat_bin }}/*
     virtualenv {{ heat_bin | dirname }} \
         {{ (ansible_pkg_mgr == 'apt') | ternary('--always-copy', '') }} \