lib-fs-resize: Prevent crash resizing FAT16 file systems

Resizing FAT16 file system crashes in libparted/fs/r/fat/resize.c
create_resize_context() because it was dereferencing NULL pointer
fs_info->info_sector to copy the info_sector.

Only FAT32 file systems have info_sector populated by fat_open() ->
fat_info_sector_read().  FAT12 and FAT16 file systems don't have an
info_sector so pointer fs_info->info_sector remains assigned NULL from
fat_alloc().  When resizing a FAT file system create_resize_context()
was always dereferencing fs_info->info_sector to memory copy the
info_sector, hence it crashed for FAT12 and FAT16.

Make create_resize_context() only copy the info_sector for FAT32 file
systems.

Reported by Christian Hesse in
https://bugzilla.gnome.org/show_bug.cgi?id=735669
tests: t3000-resize-fs.sh: Add FAT16 resizing test

Add FAT16 resizing test so that we don't regress again.
tests: t3000-resize-fs.sh: Add requirement on mkfs.vfat

Add test skipping requirement on mkfs.vfat for the FAT32 and FAT16 file
system resizing tests.  This matches existing test skipping requirement
on mkfs.hfs for the hfs+ file system.

* tests/t3000-resize-fs.sh: Also correct skip_test_ to skip_.
* tests/t-lib-helpers.sh: Also update message for requirement of hfs.
tests: Change minimum size to 256MiB

btrfs on ppc64 wants 136MiB so expand the minimum temp filesystem size
for the t1700-probe-fs test.