setup keystone using apache mod_wsgi

Allow keystone to be set up to use apache mod_wsgi as the server
instead of a standalone eventlet service.  There is a new keystone
class parameter: service_name.  The default is 'keystone', which will
set up the standalone eventlet service.  If 'httpd' is used, the
keystone class will skip creating the keystone service, which also means
no 'openstack-keystone' service.  The class 'keystone::wsgi::apache' is
then used to configure apache mod_wsgi to serve keystone.

Had to remove the File resource default in the keystone class.  When
using wsgi::apache, the apache class and other classes are included.
Since puppet uses dynamic scoping, this overrides the file resources
in those classes as well.  keystone now explicitly sets all of the
parameters in files/directory resources.

Change-Id: Ib05ac81381e169845b44b2ef7cb810a4d5db17de
Closes-Bug: #1348728