bash syntax cleanup

as per discussion in https://github.com/sovereign/sovereign/pull/504

roles/common/files/etc_cron-monthly_letsencrypt-renew

@@ -1,4 +1,5 @@
 #!/bin/bash
+set -o errexit
 # Renew all live certificates with LetsEncrypt.  This needs to run at least
 # once every three months.
 
@@ -11,8 +12,8 @@ function getDomains() {
 }
 
 service apache2 stop
-for c in `ls /etc/letsencrypt/live`; do
-  domains=$(getDomains /etc/letsencrypt/live/$c/cert.pem)
+for c in $(find /etc/letsencrypt/live/ -mindepth 1  -type d); do
+  domains=$(getDomains "$c"/cert.pem)
   /root/letsencrypt/letsencrypt-auto --renew certonly -c /etc/letsencrypt/cli.conf --domains=$domains
 done
 service apache2 start