Add wsgi_chunked_request option

This option is necessary[1] when running OpenStack's keystone on Apache.
This functionality has been merged[2] into the upstream puppetlabs-apache.

[1] https://review.openstack.org/#/c/34835/
[2] https://github.com/puppetlabs/puppetlabs-apache/pull/890

Conflicts:
	manifests/wsgi/apache.pp
	spec/classes/keystone_wsgi_apache_spec.rb

Change-Id: Ifa2cc3907252e2bafd9248a695e81f4d9444d243