poky.conf: supported distro warning update

poky.conf: supported distro warning update

* Remove Fedora 15 (no longer supported by Fedora project)
* Add upcoming Fedora 18
* Add upcoming Ubuntu 12.10
* Add CentOS 5.8 & 6.3
* Add new Poky distro name format (self-hosted / build appliance) for
  Yocto Project 1.2 / 1.3
* Update Debian squeeze to 6.0.6 (automatic update from earlier 6.0.x)
* Add openSUSE 12.2

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>