RHEL-based distros support

This patch implements initial support of RHEL-based distributions
(RHEL, CentOS, Scientific/NauLinux, Oracle Linux) as a building host.
In setup script added possibility of using of distributions flavors
array, possibility of partial description of distribution name (RHEL
and Oracle specific) and partial version numbering (accordingly new
scheme of CentOS minor version numbering).

Signed-off-by: Oleg Sadov <oleg.sadov@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>