Split hello-numThreads-1 for fixed and multiplexed tasks-per-thread.

[Not reviewed.]

The hello-numThreads-1 test was originally designed to prevent us from
counting comm layer support threads against the user thread count, as we
had once improperly done.  But it began deadlocking with CHPL_TASKS=fifo
recently, after we added a forall loop to the module initialization
code.  This happened because with FIFO's fixed relationship between
tasks and threads, and the need for a remote task to implement certain
atomics used by forall end processing, one task-hosting thread (per
locale) wasn't enough to allow progress.  To get things working again
and still retain the test's opriginal purpose, this commit splits it
into two tests.  One is run with but a single thread, for the tasking
layers which can pass it. The other is run with two threads, for fifo
tasking with its fixed tasks-per-thread model.

The commit also reorganizes things so test/multilocale/gbt looks like
its siblings.  Specifically:
- Create test/multilocale/gbt/needMultiLocales to hold tests which must
  run on multiple locales.  Give it a SKIPIF so it is not tested with
  CHPL_COMM=none and a NUMLOCALES so it is always tested with 2 locales.
  Move all the tests that were previously directly in .../gbt into
  .../gbt/needMultiLocales.
- Add a .skipif so that hello-numThreads-1 is not run with tasks=fifo.
- Add a new hello-numThreads-2, which allows two threads, and is only
  run with tasks=fifo.


git-svn-id: http://svn.code.sf.net/p/chapel/code/trunk@22159 3a8e244f-b0f2-452b-bcba-4c88e055c3ca