LU-13745 test: add splice test for lustre

LU-13745 test: add splice test for lustre

copied from xfstests with adjustment with PAGE SIZE
alignement for DIO, and codes style cleanup.

Test-Parameters: trivial envdefinitions=ONLY=425 testlist=sanity
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Change-Id: I28e83abb4a1181db20a2564a10f40ca208bb2756
Reviewed-on: https://review.whamcloud.com/39695
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>