Improve bash quoting, and other similar best practices

This patch updates the shell scripts with some of the common best
practices, which should make them more resilient to unusual failures and
unexpected environments (in particular, directories with spaces).

Most of these were identified by shellcheck.

test/stress.sh

@@ -1,16 +1,16 @@
 #!/bin/bash
 
 set -e
-. $(dirname ${0})/util/lib.sh
+. "$(dirname "$0")/util/lib.sh"
 
 init
 
 FAILED=0
 
 for i in stress-*; do
-	echo $i ...
-	setsid -w $i/run.sh
-	FAILED=$(( $FAILED + $? ))
+	echo "$i ..."
+	setsid -w "$i/run.sh"
+	FAILED=$(( FAILED + $? ))
 	echo
 done