LU-80 tests: make lfs_migrate script executable

LU-80 tests: make lfs_migrate script executable

When running sanity.sh test_56w from the build tree, the test fails
because lfs_migrate does not have execute permission set.  Set the
execute permissions on this script in the build tree.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I4af5d7ff4b41353d2e73937292020505ef8de0d9
Reviewed-on: http://review.whamcloud.com/3020
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>