LU-2405 tests: verify off-by-one symlink length fix

LU-2405 tests: verify off-by-one symlink length fix

Add regression test for off-by-one bug in symlink code. Ensures boundary
condition of 60 character symlinks are readable after creation.

original commit 6c3606b79a4c25946255a680f79ff2d58df66bbc

Whamcloud-bug-id: LU-2241
Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: I4264558a5b638e73e7631b988b05b92405d13288
Reviewed-on: http://review.whamcloud.com/4711
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>