cpuid: move the CPUID levelling stuff to the xenops interface
vss: remove the xenstore-based vss client from xapi

This needs to be a separate tool which can be invoked from xapi.
xenops: add the unix domain socket to the interface
memory: read host reserved/free memory via the memory control interface (ie via squeezed)

In the event that squeezed isn't running, we assume that overheads are 0
so we will attempt to start VMs and see what happens.
xapi: remove dead code

Signed-off-by: David Scott <dave.scott@eu.citrix.com>