d/libvirt-doc.doc: install rendered docs

- new doc build properly puts all we need into
  debian/tmp/usr/share/doc/libvirt/html/.
  Simplifies many rules (src:docs mostly has .in files nowadays)
- devhelp became devguide and is installed there
- internals (html.in) rendered and installed thre
- kbase (rst) is rendered and installed there
- logos are installed there
- examples directory is there
- this change does not seem to re-introduce
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=492075


- dh_installdocs adds package name, so pull from libvirt/*

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>