LU-3606 fsx: Add fallocate operation to fsx

LU-3606 fsx: Add fallocate operation to fsx

This patch updates Lustre fsx(File system exerciser)
to handle fallocate calls. There is no need to change
any existing test case using "fsx" binary as with this
fsx version the 'fallocate' call will simply be skipped
as "Operation not supported".

Test-Parameters: trivial testlist=sanity,sanityn,sanity-dom
Signed-off-by: Swapnil Pimpale <spimpale@ddn.com>
Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Abrarahmed Momin <abrar.momin@gmail.com>
Signed-off-by: Arshad Hussain <arshad.super@gmail.com>
Change-Id: I81649d00984257b1785e763ab5c00d570eb412f9
Reviewed-on: https://review.whamcloud.com/37273
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>