gitignore: Ignore more files
gitignore: Ignore more files

Noticed while playing around with PDF generation.

Change-Id: I6e2273cb20247cbb85b03e1abe1b8924f708e12b
Signed-off-by: Stephen Finucane <492121341a95b3c3aab646bed44634f739dd019b@redhat.com>

openstack/openstackdocstheme,openstack/openstackdocstheme,openstack/openstackdocstheme,openstack/openstackdocstheme