test_pg.sh: fail the script if compiling tests fails

wait without arguments always succeeds, with jobspec it returns the exit
code of that job.

test_pg.sh

@@ -17,7 +17,7 @@ trap 'start_pg_cleanup' EXIT INT
 createdb goatherd_test
 
 echo Waiting for compile to finish
-wait
+wait %1
 
 echo
 echo ===== Tests =====