Change the way arithmetic operations are performed in system test shell
scripts from using `expr` to `$(())`. This ensures that updating the
variable won't end up with a non-zero exit code, which would case the
script to exit prematurely when `set -e` is in effect.
The following replacements were performed using sed in all text files
(git grep -Il '' | xargs sed -i):
s/status=`expr $status + $ret`/status=$((status + ret))/g
s/n=`expr $n + 1`/n=$((n + 1))/g
s/t=`expr $t + 1`/t=$((t + 1))/g
s/status=`expr $status + 1`/status=$((status + 1))/g
s/try=`expr $try + 1`/try=$((try + 1))/g
4d42bdc245