Added wiki instructions for Openstack on F17

[Alan Pevec]

Hi Cole,

thanks for starting this! One important notice (I've edited the wiki
to reflect this):
in F17 default nova.conf changed from flagfile to configfile
(ini-style) format
http://pkgs.fedoraproject.org/gitweb/?p=openstack-nova.git;a=commitdiff;h=8e2e091558799cc088893df4bf83808c63502975

so all echo >> nova.conf will now use openstack-config-set (script
I've currently put in openstack-keystone RPM and should move to
openstack-common when that's ready upstream)
e.g.
 echo '--libvirt_type=qemu' | sudo tee -a /etc/nova/nova.conf
to
 openstack-config-set /etc/nova/nova.conf DEFAULT libvirt_type qemu

Thanks,
Alan