Rework chpl_getNum{Cores,PUs}OnThisNode().

This standardizes naming, making the following changes:
  chpl_getNumCoresOnThisNode() --> chpl_getNumPhysCpusOnThisNode()
  chpl_getNumPUsOnThisNode() --> chpl_getNumLogCpusOnThisNode()

It also adds an argument to both of these, for callers to indicate
whether they want information about all the CPU resources that are
present on the node, or only the ones to which the process has access
(due to kernel affinity restrictions, etc.).

I ran the maxTaskPar test on this change with CHPL_TASKS=qthreads,
CHPL_TASKS=qthreads and CHPL_LOCALE_MODEL=numa, CHPL_TASKS=fifo,
CHPL_TASKS=massivethreads, and CHPL_TASKS=muxed.
Food for thought, nothing you have to change: but is there a reason we don't use hwloc to gather this info. It's pretty simple for now but if we imagine it getting more complicated it seems like we're duplicating effort?