LU-16025 llite: adjust read count as file got truncated

LU-16025 llite: adjust read count as file got truncated

File read will not notice the file size truncate by another node,
and continue to read 0 filled pages beyond the new file size.

This patch add a confinement in the read to prevent the issue and
add a test case verifying the fix.

Lustre-change: https://review.whamcloud.com/47896
Lustre-commit: 4468f6c9d92448cb72c5a616ec74653e83ee8e10

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: Ie51ba09201a1ca1464c3a3892d367590e978ee34
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/48848
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>