amount a physical has is stored in the node types table, and the
per-vm memory requirement is stored in the nodes table. ptopgen
adds up usage, and subtracts from the total for the ptop file.
The vtop number comes from a virt_node_attribute table, and we
pass this through to the client side. Note that this is less
important for openvz, more so for XEN.

In the NS file:

	tb-set-node-memory-size $node 1024

Number is in MBs. The mapper defaults this to 128 for openvz and 256
for xen. Maximum is hardwired to 256 and 512 respectively. Need to
think about a good way to configure this in.