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-02-connections/run.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 set -e
-. $(dirname ${0})/../util/lib.sh
+. "$(dirname "$0")/../util/lib.sh"
 
 init
 
@@ -14,22 +14,22 @@ mkdir -p .logs
 chasquid -v=-1 --logfile=.logs/chasquid.log --config_dir=config &
 wait_until_ready 1025
 
-echo Peak RAM: `chasquid_ram_peak`
+echo "Peak RAM: $(chasquid_ram_peak)"
 
 # Set connection count to (max open files) - (leeway).
 # We set the leeway to account for file descriptors opened by the runtime and
 # listeners; 20 should be enough for now.
 # Cap it to 2000, as otherwise it can be problematic due to port availability.
-COUNT=$(( `ulimit -n` - 20 ))
+COUNT=$(( $(ulimit -n) - 20 ))
 if [ $COUNT -gt 2000 ]; then
 	COUNT=2000
 fi
 
 if ! conngen -logtime -addr=localhost:1025 -count=$COUNT; then
 	tail -n 1 .logs/chasquid.log
-	fail
+	fail "conngen error"
 fi
 
-echo Peak RAM: `chasquid_ram_peak`
+echo "Peak RAM: $(chasquid_ram_peak)"
 
 success