vchoi_fork

Make all VFD SWMR test writers wait for a signal before closing
their HDF5 file, and always send that signal after the readers
are finished.  Carve out an exception, though, for the expand/shrink
test, where vfd_swmr_writer is used to initialize the file.

Move await_signal() to vfd_swmr_common.c for sharing with all of
the writers.

Add to vfd_swmr_writer a command-line option flag, -W, that stops
it from waiting for a signal before closing the HDF5 file and
quitting.  While I'm here, rewrite the option processing to use
getopt(3).

Block signals early on in the VFD SWMR writers so that testvfdswmr.sh
cannot kill a slow writer before it's finished writing.

In the VFD SWMR test-readers and -writers, disable the chunk cache so that
dataset-writes don't languish in writers and readers don't re-read stale
data.

Add a new source file, vfd_swmr_common.c, and update Makefile.am Also update
the CMake configuration for VFD SWMR---I haven't tested it, so it may not be
right.

Delete some dead timing code in vfd_swmr_sparse_writer.c.