Add three options to barclamp UI and handle them in chef too

We add support for the auto_assign_floating_ip option for nova-network,
and for cpu_allocation_ratio/ram_allocation_ratio options for
nova-scheduler (ram_allocation_ratio was already a chef attribute, but
with a value not changeable in the barclamp).

Signed-off-by: Vincent Untz <vuntz@suse.com>