Update Httpd configuration docs for sites-available/enabled
Update Httpd configuration docs for sites-available/enabled

Newer releases of Apache Httpd server prefer to use sites-available /
sites-enabled configuration directories, but the Apache setup
documentation was still using conf.d. This change updates the Apache
setup documentation to use the preferred method.

Change-Id: I00a4cef2e4194b07f12ed0c0f6c584f236771a00

idjaw/keystone,dims/keystone,himanshu-setia/keystone,takeshineshiro/keystone,jamielennox/keystone,openstack/keystone,rajalokan/keystone,klmitch/keystone,maestro-hybrid-cloud/keystone,rajalokan/keystone,openstack/keystone,cernops/keystone,ajayaa/keystone,openstack/keystone,takeshineshiro/keystone,roopali8/keystone,himanshu-setia/keystone,mahak/keystone,mahak/keystone,roopali8/keystone,dims/keystone,ilay09/keystone,maestro-hybrid-cloud/keystone,jonnary/keystone,rajalokan/keystone,klmitch/keystone,mahak/keystone,ilay09/keystone,idjaw/keystone,ajayaa/keystone,ilay09/keystone,jamielennox/keystone,jonnary/keystone,cernops/keystone