hdf5_msb

Don't use FILENAME and FILENAME[0] because that looks like worrisome
macro magic.  Use namebases and namebase, instead.

Extract a bunch of copy-and-paste VFD SWMR setup into a new subroutine,
swmr_fapl_augment().

Make sure that the metadata reads all-0s until it reads all -1s.
Extract a subroutine, vfd_read_each_equals(), that reads and compares a
region with one of its arguments.

Rename from test_basic_metadata_handling() to
test_metadata_delay_basic(), since that gets at what we're testing
better.

Don't perform an H5PB_flush(), it's not necessary for this test because
H5Fvfd_swmr_end_tick() has done essentially the same thing.