LU-10059 tests: sanityn 32a error messages

LU-10059 tests: sanityn 32a error messages

There are three checks for file size in sanityn test 32a
that, if they fail, have the same error message
"wrong file size".  Let's add additional information to
the error messages to help distinguish the different errors.

Test-Parameters: trivial testlist=sanityn
Signed-off-by: James Nunez <jnunez@whamcloud.com>
Change-Id: I71aae8de67125d5be93c4fb4728b2c20d26df49c
Reviewed-on: https://review.whamcloud.com/40496
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.super@gmail.com>
Reviewed-by: Vikentsi Lapa <vlapa@whamcloud.com>