Honor random/zero/compressible settings for filling an initial file

Honor random/zero/compressible settings for filling an initial file

Right now we only do that for when the job writes, do it for the
initial setup as well. Otherwise you just get zero filled files
initially, which might not be what you want.

Also fixes a bug with compression if compress_chunk isn't set.

Signed-off-by: Jens Axboe <axboe@kernel.dk>