[autogenerate_config_docs] use filename tags to mark filenames
[autogenerate_config_docs] use filename tags to mark filenames

According to the markup conventions the filename tag should be
used to mark filenames.

Change-Id: I658b060df81ac62d68e6aafe3db40d71cb7e79cb

savinash47/openstack-doc-tools,openstack/openstack-doc-tools,openstack/openstack-doc-tools,savinash47/openstack-doc-tools,savinash47/openstack-doc-tools