improve WSGI configuration

This patch improves the WSGI support:
 - introduce a wsgi_user and wsgi_group to avoid confusion with
   apache_user and apache_group
 - ensure openstack-dashboard.conf will not conflict with apache::vhost
 - ensure the WSGI user can write in the log file
 - ability to define the number of WSGI process/thread
 - disable the SSL vhost if needed
 - create the /static alias using puppet-apache "alias" key

Closes-bug: #1265169

Change-Id: I39b52b2bc51ba04d59de81dc45b5a4ad82d0dc2c
Merge "improve WSGI configuration"