HPCC-9814 Show N/A when a memory node is not available

Existing code shows '0%' SWAP when a SWAP is not configured on
a system. It caused some misleading. This fix checks the total
memory size for a memory node. If the size is zero, it shows N/A.

Signed-off-by: Kevin Wang <kevin.wang@lexisnexis.com>
Merge pull request #4712 from wangkx/swap_0

HPCC-9814 Show N/A when a memory node is not available

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>