Add an RPM spec file and customize ansible roles_path

Install roles under /usr/local/share/kubespray/roles,
playbooks - /usr/local/share/kubespray/playbooks/,
ansible.cfg and inventory group vars - into /etc/kubespray.
Ship README and an example inventory as the package docs.
Update the ansible.cfg to consume the roles from the given path,
including virtualenvs prefix, if defined.

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>