CA-34549: make the host chooser use the precomputed memory_overhead for consistency.
CA-34549: make the host chooser use the precomputed memory_overhead for consistency.

Now it should be possible to make a single large VM by:
* subtracting the host memory-overhead from memory-total
* subtracting dom0's memory-actual and memory-overhead
* subtracting the overhead of a new VM
* make the new VM use all remaining memory

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

johnelse/xcp-rrdd,djs55/xcp-rrdd,simonjbeaumont/xcp-rrdd,johnelse/xcp-rrdd,djs55/xcp-networkd,robhoes/squeezed,koushikcgit/xcp-rrdd,koushikcgit/xcp-networkd,djs55/xcp-rrdd,sharady/xcp-networkd,djs55/squeezed,djs55/xcp-networkd,koushikcgit/xcp-networkd,simonjbeaumont/xcp-rrdd,koushikcgit/xcp-rrdd,sharady/xcp-networkd,koushikcgit/xcp-rrdd