* move rst files from doc/man/8 into man/8
* extract man_pages setting for sphinx from doc/conf.py to man/conf.py
* generate all man pages in `make install`
* add python-sphinx to Build-Depends
* check for sphinx-build in `configure`
* run changed rst files through sphinx-build in `make check`
Signed-off-by: Kefu Chai <kchai@redhat.com>