LU-9771 flr: make sure init size work

LU-9771 flr: make sure init size work

Lustre allows to create a file with empty layout, and truncate it
up with non-zero file size. The size should be applied later after
a layout is attached.

Test-Parameters: testlist=sanity-flr

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Ie645f8172e98426a531eb2d9ffdcbec8f73f3731
Reviewed-on: https://review.whamcloud.com/29581
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>