Fix #450 - compute numa nodes and distances properly

[lars-t-hansen]

OK, so strategy:

• look for the distance files for nodes up to numsockets-1
• if we find them, they should together make a square matrix
• and the number of nodes we found is exposed as a new numa_nodes field in the output
• if we don't find them, we do not error out but just return an empty value

[lars-t-hansen]

@2maz, gentle review ping.

[2maz]

LGTM