support other components using apache mod_wsgi

Keystone is moving to use apache mod_wsgi instead of standalone
eventlet daemon.  Packstack should support deployment of keystone
using this model.  A new command line switch --keystone-service-name
is added, and a new config parameter CONFIG_KEYSTONE_SERVICE_NAME
is added.  If this is set to 'httpd', keystone will be set up to use
apache mod_wsgi, otherwise, it will be a standalone eventlet service.

There is some common apache configuration that must be done by
every module that uses apache.  There is a new class in packstack
called packstack::apache_common.  Each component that uses apache
must call "include packstack::apache_common".  This ensures that
a subsequent component manifest will not wipe out apache
configuration created by a previous component manifest or the initial
apache configuration created by prescript.pp.

Change-Id: I73b853507dffb2540638182f3072e65e4d7ad485
Closes-Bug: #1348732
Merge "support other components using apache mod_wsgi"