Alternate scheduler for use with OpenStack Nova based on nova.scheduler.simple.SimpleScheduler that doesn't oversubscribe memory

The SimpleScheduler massively oversubscribes memory without regard. The check in Diablo doesn't work with libvirt/kvm, this fixes the bug. It is a simple and straight-forward, iterative fix. There is a better solution being introduced in Essex, currently in review.

This should be used by anyone using libvirt/kvm and the SimpleScheduler on OpenStack Nova (Diablo).

tests.py should be run as part of the nova unittests.

Just run python setup.py install

In nova.conf set the following flags:

--scheduler_driver=cloudscaling.nova.scheduler.simple.SimpleScheduler
--cs_host_reserved_memory_mb=1024

Where cs_host_reserved_memory_mb specifies how much memory ( in megabytes) to reserve for the host