xfsqa: make hole tests independent of speculative allocation patterns

xfsqa: make hole tests independent of speculative allocation patterns

Many of the "count-the-holes" tests (008, 012, etc) do writes that extend the
file and hence allocation patterns are dependent on speculative allocation
beyond EOF behaviour. Hence if we change that behaviour, these tests all fail
because there is a different pattern of holes.

Make the tests independent of EOF preallocation behaviour by first truncating
the file to the size the test is defined to use. This prevents speculative
prealocation from occurring, and hence changes in such behaviour will not cause
the tests to fail.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>