Summary:
Fix a minor usage problem in a test script.
The format.sh test script doesn't correctly handle relative "home" directories:
% ./format.sh -j 1 -F -h WT_TEST format.sh: starting job in /home/ubuntu/wiredtiger/test/format/WT_TEST /home/ubuntu/wiredtiger/test/format/WT_TEST/RUNDIR.1 (Thu Jan 16 19:15:10 UTC 2020) ./format.sh: line 392: $log: ambiguous redirect