LU-5637 tests: set filefrag blocksize to 1024

LU-5637 tests: set filefrag blocksize to 1024

If blocksize for filefrag is unspecified it defaults to 1024 bytes.
But for example at SL7 blocksize defaults is 4096.
Set it to 1024 to have everywhere the same results.

Test-Parameters: trivial envdefinitions=ONLY=130 testlist=sanity
Change-Id: I550446c6c7c0b85aa769f0f8a7575a6d33b2dc4b
Cray-bug-id: MRP-2933
Signed-off-by: Sergey Cheremencev <c17829@cray.com>
Reviewed-on: https://review.whamcloud.com/30391
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Minh Diep <minh.diep@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>