tests: factor 350 fail=0 initializations into test-lib.sh

Run this command to remove the factored-out "fail=0" lines.
perl -ni -e '/^fail=0$/ or print' $(g grep -l '^fail=0$')
* tests/test-lib.sh: Initialize fail=0 here, not in 300+ scripts.
* tests/...: nearly all bourne shell scripts
Suggested by Eric Blake.

tests/misc/sort-continue

@@ -31,7 +31,6 @@ for i in $(seq 31); do
   echo $i | tee -a in > __test.$i || framework_failure
 done
 
-fail=0
 
 (
  ulimit -n 6