EX-2745 tests: reduce file size for hot-pools.sh test 56

EX-2745 tests: reduce file size for hot-pools.sh test 56

This patch reduces the file size for hot-pools.sh test 56
by adjusting lpurge freelo and freehi options so as to
trigger lpurge after writing files with smaller size.

Test-Parameters: trivial testlist=hot-pools,hot-pools \
serverextra_install_params="--lipe-job lipe --lipe-build 0 -k zfs"

Test-Parameters: trivial testgroup=review-dne-part-2 \
serverextra_install_params="--lipe-job lipe --lipe-build 0 -k zfs"

Change-Id: I15c3a11e6453ec24d11c188ae82a980587259e80
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/42027
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>