generic: add generic test for fallocate zero range

generic: add generic test for fallocate zero range

This is based on xfs/242. This is very similar to ext4/001 however this
test has some tweaks to make it work test zero range on generic file
system. This includes turning off ext4 extents zeroout and disabling
the test for xfs on systems where PAGE_SIZE > 4096.

It is testing extent tree manipulation with fallocate zero range
operation.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>