[parted-devel] 8 small changes

[Jim Meyering]

I'm going to push these today.
FWIW, they were prompted by still more changes
that I'm working on, that might help us get much
better test coverage for s390x/dasd.

These are mostly clean-up and test-adding changes,
but do include two small bug fixes:

      ped_disk_type_get_next: fix a const-correctness bug
      tests: rewrite t0202 to use new framework
      tests: weaken t0202-gpt-pmbr to assume a preexisting GPT table
      dvh: replace open-coded dvh_clobber with equivalent, shorter code
 FIX  gpt_probe: don't attempt to read beyond end of a very small disk
 FIX  linux_read: give a proper diagnostic for an "end of file" error
      tests: t0000-basic.sh: minor correction
      gpt: greatly simply gpt_clobber; minor semantic change, too